"'Conjoined twins" are identical twins joined in utero. An extremely rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher incidence in Southeast Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.

Two contradicting theories exist to explain the origins of conjoined twins. The more generally accepted theory is "fission", in which the fertilized egg splits partially. The other theory, no longer believed to be the basis of conjoined twinning, is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together. Conjoined twins share a single common chorion, placenta, and amniotic sac, although these characteristics are not exclusive to conjoined twins as there are some monozygotic but non-conjoined twins who also share these structures in utero.

The most famous pair of conjoined twins was Chang and Eng Bunker (Thai: อิน-จัน, In-Chan) (1811–1874), Thai brothers born in Siam, now Thailand. They traveled with P.T. Barnum's circus for many years and were labeled as the Siamese twins. Chang and Eng were joined at the torso by a band of flesh, cartilage, and their fused livers. In modern times, they could have been easily separated. Due to the brothers' fame and the rarity of the condition, the term "Siamese twins" came to be used as a synonym for conjoined twins.

Conjoined twins are typically classified by the point at which their bodies are joined. The most common types of conjoined twins are:

- Thoraco-omphalopagus (28% of cases): Two bodies fused from the upper chest to the lower chest. These twins usually share a heart, and may also share the liver or part of the digestive system.

- Thoracopagus (18.5%): Two bodies fused from the upper thorax to lower belly. The heart is always involved in these cases. As of 2015, separation of a genuinely shared heart has not offered survival to two twins; a designated twin may survive if allotted the heart, sacrificing the other twin.

- Omphalopagus (10%): Two bodies fused at the lower abdomen. Unlike thoracopagus, the heart is never involved in these cases; however, the twins often share a liver, digestive system, diaphragm and other organs.

- Parasitic twins (10%): Twins that are asymmetrically conjoined, resulting in one twin that is small, less formed, and dependent on the larger twin for survival.

- Craniopagus (6%): Fused skulls, but separate bodies. These twins can be conjoined at the back of the head, the front of the head, or the side of the head, but not on the face or the base of the skull.

Other less-common types of conjoined twins include:

- Syncephalus: One head with a single face but four ears, and two bodies.

- Cephalothoracopagus: Bodies fused in the head and thorax. In this type of twins, there are two faces facing in opposite directions, or sometimes a single face and an enlarged skull.

- Xiphopagus: Two bodies fused in the xiphoid cartilage, which is approximately from the navel to the lower breastbone. These twins almost never share any vital organs, with the exception of the liver. A famous example is Chang and Eng Bunker.

- Ischiopagus: Fused lower half of the two bodies, with spines conjoined end-to-end at a 180° angle. These twins have four arms; one, two, three or four legs; and typically one external set of genitalia and anus.

- Omphalo-Ischiopagus: Fused in a similar fashion as ischiopagus twins, but facing each other with a joined abdomen akin to omphalopagus. These twins have four arms, and two, three, or four legs.

- Parapagus: Fused side-by-side with a shared pelvis. Twins that are dithoracic parapagus are fused at the abdomen and pelvis, but not the thorax. Twins that are diprosopic parapagus have one trunk and two faces. Twins that are dicephalic parapagus have one trunk and two heads, and have two (dibrachius), three (tribrachius), or four (tetrabrachius) arms.

- Craniopagus parasiticus: Like craniopagus, but with a second bodiless head attached to the dominant head.

- Pygopagus (Iliopagus): Two bodies joined at the pelvis.

- Rachipagus: Twins joined along the dorsal aspect (back) of their bodies, with fusion of the vertebral arches and the soft tissue from the head to the buttocks

Ilona and Judit Gófitz (Hungarian: "Gófitz Ilona" és "Judit"; in contemporary publications: "Helen" and "Judith of Szőny"), also known as the Hungarian Sisters, were conjoined twins from Szőny, Hungary who lived from October 19, 1701 to February 8, 1723. In the image they appear to be pygopagus.

Republican marriage () was a method of execution that allegedly occurred in Nantes during the Reign of Terror in Revolutionary France and "involved tying a naked man and woman together and drowning them". This was reported to have been practised during the drownings at Nantes ("noyades") that were ordered by local Jacobin representative-on-mission Jean-Baptiste Carrier between November 1793 and January 1794 in the city of Nantes. Most accounts indicate that the victims were drowned in the Loire River, although a few sources describe an alternative means of execution in which the bound couple is run through with a sword, either before, or instead of drowning.

The earliest reports of such "marriages" date from 1794, when Carrier was tried for his crimes, and they were soon cited by contemporary counter-revolutionary authors such as Louis-Marie Prudhomme and Louis Gabriel Ambroise de Bonald.

The phenomenon known as Beatlemania originated in the United Kingdom, birthplace of the Beatles, when the band first realised enormous popularity there in 1963. Returning in 1962 from a highly formative two-year residency in Germany, the Beatles achieved a commercial breakthrough with their second UK single release, "Please Please Me" early in 1963, but gained "Superstar" status with the release of "She Loves You" later that year. There followed an almost non-stop series of concerts and tours, attended with feverish enthusiasm across the UK, for the whole of the following year. The Beatles' popularity in the UK came to exceed even that of the notable American artists Tommy Roe, Chris Montez and Roy Orbison, whose UK chart success at the time did not keep them from being overshadowed by the Beatles during their 1963 nationwide tours with the lower-billed band — an achievement previously unknown for a UK act.

With intense media interest in the Beatles during 1963, the year was also taken up with TV shows, press interviews and a weekly radio show. Despite these demands the band found time for many sessions in the recording studio, releasing two albums and four singles during the year. 1963 was also the year when Lennon's son Julian was born.

By the end of 1963, Beatlemania would begin to spread internationally. The single "I Want to Hold Your Hand" entered the US charts on 18 January 1964, selling one-and-a-half million copies in under three weeks, and the following month the Beatles made their first visit to America. The great interest in the Beatles brought about a major change in US attitudes to popular music and marked the start of the phenomenon known as the British Invasion.

Cryptomnesia occurs when a forgotten memory returns without it being recognized as such by the subject, who believes it is something new and original. It is a memory bias whereby a person may falsely recall generating a thought, an idea, a tune, or a joke, not deliberately engaging in plagiarism but rather experiencing a memory as if it were a new inspiration.

Mental and emotional symptoms of lilapsophobia include

- Obsessive thoughts

- Difficulty thinking

- Feeling of unreality or being detached

- Fear of losing control or going crazy

- Anticipatory anxiety

- Terror

- Desire to flee or hide

Physical symptoms of lilapsophobia include

- Dizziness, shaking, palpitations, lightheaded, or faint

- Shortness of breath

- Accelerated heartbeat

- Chest pain or discomfort

- Shaking

- Feeling of choking

- Sweating

- Nausea

- Numbness or tingling sensations

Many lilapsophobes also suffer autophobia, fear of being alone. Sufferers often make arrangements with people they know to help soothe the fear.

Like many phobias, lilapsophobia is caused by an unwanted experience, specifically tornadoes or hurricanes that cause injuries, destruction, or loss of loved ones to self or others they know. People who survive those storms should seek professional advice, especially to determine if a person is suffering post-traumatic stress disorder. This phobia can even be caused by learning news about tornadoes or hurricanes using the media, like television, internet, radio, or newspaper, even though they happened far away from homes.

If a person learns that someone in the family has the phobia, then that person is more likely to suffer from it.

Islamophobia is an intense fear or hatred of, or prejudice against, the Islamic religion or Muslims, especially when seen as a geopolitical force or the source of terrorism.

The term was first used in the early 20th century and it emerged as a neologism in the 1970s, then it became increasingly salient during the 1980s and 1990s, and it reached public policy prominence with the report by the Runnymede Trust's Commission on British Muslims and Islamophobia (CBMI) entitled "Islamophobia: A Challenge for Us All" (1997). The introduction of the term was justified by the report's assessment that "anti-Muslim prejudice has grown so considerably and so rapidly in recent years that a new item in the vocabulary is needed".

The causes and characteristics of Islamophobia are still debated. Some commentators have posited an increase in Islamophobia resulting from the September 11 attacks, some from multiple terror attacks in Europe and the United States, while others have associated it with the increased presence of Muslims in the United States and in the European Union. Some people also question the validity of the term. The academics S. Sayyid and Abdoolkarim Vakil maintain that Islamophobia is a response to the emergence of a distinct Muslim public identity globally, the presence of Muslims is in itself not an indicator of the degree of Islamophobia in a society. Sayyid and Vakil maintain that there are societies where virtually no Muslims live but many institutionalized forms of Islamophobia still exist in them.

Transmisogyny (sometimes trans-misogyny) is the intersection of transphobia and misogyny. Transphobia is defined as "the irrational fear of, aversion to, or discrimination against transgender or transsexual people". Misogyny is defined as "a hatred of women". Therefore, transmisogyny includes negative attitudes, hate, and discrimination of transgender or transsexual individuals who fall on the feminine side of the gender spectrum, particularly transgender women. The term was coined by Julia Serano in her 2007 book "Whipping Girl" and used to describe the unique discrimination faced by trans women because of "the assumption that femaleness and femininity are inferior to, and exist primarily for the benefit of, maleness and masculinity", and the way that transphobia intensifies the misogyny faced by trans women (and vice versa). It is said many trans women experience an additional layer of misogyny in the form of fetishization; Serano talks about how society views trans women in certain ways that sexualize them, such as them transitioning for sexual reasons, or ways where they’re seen as sexually promiscuous.Transmisogyny is a central concept in transfeminism and is commonly referenced in intersectional feminist theory. That trans women's femaleness (rather than only their femininity) is a source of transmisogyny is denied by certain radical feminists, who claim that trans women are not female.

Transphobia is a range of negative attitudes, feelings or actions toward transgender or transsexual people, or toward transsexuality. Transphobia can be emotional disgust, fear, violence, anger or discomfort felt or expressed towards people who do not conform to society's gender expectations. It is often expressed alongside homophobic views and hence is often considered an aspect of homophobia. Transphobia is a type of prejudice and discrimination similar to racism and sexism, and transgender people of color are often subjected to all three forms of discrimination at once.

Child victims of transphobia experience harassment, school bullying, and violence in school, foster care, and social programs. Adult victims experience public ridicule, harassment including misgendering, taunts, threats of violence, robbery, and false arrest; many feel unsafe in public. A high percentage report being victims of sexual violence. Some are refused healthcare or suffer workplace discrimination, including being fired for being transgender, or feel under siege by conservative political or religious groups who oppose laws to protect them. There is even discrimination from some people within the movement for the rights of gender and sexual minorities.

Besides the increased risk of violence and other threats, the stress created by transphobia can cause negative emotional consequences which may lead to substance abuse, running away from home (in minors), and a higher rate of suicide.

In the Western world, there have been gradual changes towards the establishment of policies of non-discrimination and equal opportunity. The trend is also taking shape in developing nations. In addition, campaigns regarding the LGBT community are being spread around the world to improve acceptance; the "Stop the Stigma" campaign by the UN is one such development.

Radiophobia is an obsessive fear of ionizing radiation, in particular, fear of X-rays. While in some cases radiation may be harmful (i.e. radiation-induced cancer, and acute radiation syndrome), the effects of poor information, understanding, or a traumatic experience may cause unnecessary or even irrational fear. The term is also used in a non-medical sense to describe the opposition to the use of nuclear technology (i.e. nuclear power) arising from concerns disproportionately greater than actual risks would merit.

Transsexual people experience a gender identity that is inconsistent with, or not culturally associated with, their assigned sex, and desire to permanently transition to the gender with which they identify, usually seeking medical assistance (including hormone replacement therapy and other sex reassignment therapies) to help them align their body with their identified sex or gender.

"Transsexual" is generally considered a subset of "transgender", but some transsexual people reject the label of "transgender". A medical diagnosis of gender dysphoria can be made if a person expresses a desire to live and be accepted as a member of their identified sex, and if a person experiences impaired functioning or distress as a result of their gender identity.

Irlen syndrome, occasionally referred to as scotopic sensitivity syndrome (SSS) or Meares-Irlen syndrome, very rarely as asfedia, and recently also as visual stress, is a proposed disorder of vision.

Deafblindness is the condition of little or no useful sight and little or no useful hearing. Educationally, individuals are considered to be deaf-blind when the combination of their hearing and sight loss causes such severe communication and other developmental and educational needs that they require significant and unique adaptations in their educational programs. Helen Keller was one such individual.

Homophobia encompasses a range of negative attitudes and feelings toward homosexuality or people who are identified or perceived as being lesbian, gay, bisexual or transgender (LGBT). It has been defined as contempt, prejudice, aversion, hatred or antipathy, may be based on irrational fear, and is often related to religious beliefs.

Homophobia is observable in critical and hostile behavior such as discrimination and violence on the basis of sexual orientations that are non-heterosexual. Recognized types of homophobia include "institutionalized" homophobia, e.g. religious homophobia and state-sponsored homophobia, and "internalized" homophobia, experienced by people who have same-sex attractions, regardless of how they identify.

Negative attitudes toward identifiable LGBT groups have similar yet specific names: lesbophobia is the intersection of homophobia and sexism directed against lesbians, biphobia targets bisexuality and bisexual people, and transphobia targets transgender and transsexual people and gender variance or gender role nonconformity. According to 2010 Hate Crimes Statistics released by the FBI National Press Office, 19.3 percent of hate crimes across the United States "were motivated by a sexual orientation bias." Moreover, in a Southern Poverty Law Center 2010 "Intelligence Report" extrapolating data from fourteen years (1995–2008), which had complete data available at the time, of the FBI's national hate crime statistics found that LGBT people were "far more likely than any other minority group in the United States to be victimized by violent hate crime."

The term "homophobia" and its usage have been criticized by several sources as unwarrantedly pejorative

Macrophilia is a fascination with or a sexual fantasy involving giants, more commonly expressed as giantesses (female giants). It is typically a male fantasy, with the male playing the "smaller" part—entering, being dominated, or being eaten by the larger woman. Others involve partners who naturally have a significant difference in size.

The Dorian Gray syndrome arises from the concurring and overlapping clinical concepts of the narcissistic personality, dysmorphophobia, and paraphilia. Psychodynamically, the man afflicted with DGS presents an interplay among his narcissistic tendencies ("timeless beauty"), his arrested development (inability to psychologically mature), and his use of "medical lifestyle" products and services — hair restoration, drugs (for impotence, weight-loss, and mood modification), laser dermatology, and plastic surgery — in order to remain young.

Although the DGS patient displays diagnostic features of said mental disorders, the syndrome describes a common, underlying psychodynamics of mental illness, which is characterized by narcissistic defences against time-dependent maturation, expressed by actively seeking the timeless beauty of youth. The article "Das Dorian Gray syndrom" (2005) reported that approximately 3.0 per cent of the population of Germany present features of the Dorian Gray syndrome.

The Irlen Method uses coloured overlays and tinted lenses in the form of glass or contact lenses. The method is intended to reduce or eliminate perceptual processing errors; it is claimed the resultant retiming of visual signals in the brain improves the reading difficulties associated with scotopic sensitivity syndrome.

The fear of crime refers to the fear of being a victim of crime as opposed to the actual probability of being a victim of crime.

The fear of crime, along with fear of the streets and the fear of youth, is said to have been in Western culture for "time immemorial". While fear of crime can be differentiated into public feelings, thoughts and behaviors about the personal risk of criminal victimization, distinctions can also be made between the tendency to see situations as fearful, the actual experience while in those situations, and broader expressions about the cultural and social significance of crime and symbols of crime in people's neighborhoods and in their daily, symbolic lives.

Importantly, feelings, thoughts and behaviors can have a number of functional and dysfunctional effects on individual and group life, depending on actual risk and people's subjective approaches to danger. On a negative side, they can erode public health and psychological well-being; they can alter routine activities and habits; they can contribute to some places turning into 'no-go' areas via a withdrawal from community; and they can drain community cohesion, trust and neighborhood stability. Some degree of emotional response can be healthy: psychologists have long highlighted the fact that some degree of worry can be a problem-solving activity, motivating care and precaution, underlining the distinction between low-level anxieties that motivate caution and counter-productive worries that damage well-being.

Factors influencing the fear of crime include the psychology of risk perception, circulating representations of the risk of victimization (chiefly via interpersonal communication and the mass media), public perceptions of neighborhood stability and breakdown, the influence of neighbourhood context, and broader factors where anxieties about crime express anxieties about the pace and direction of social change. There are also some wider cultural influences. For example, some have argued that modern times have left people especially sensitive to issues of safety and insecurity.

The diagnostic criteria for Dorian Gray syndrome are:

- Signs of dysmorphophobia

- Arrested development (inability to mature)

- Using at least two different medical-lifestyle products and services:

- Hair-growth restoration (e.g. finasteride)

- Antiadiposita to lose weight (e.g. orlistat)

- Anti-impotence drugs (e.g. sildenafil)

- Anti-depressant drugs (e.g. fluoxetine)

- Cosmetic dermatology (e.g. laser resurfacing)

- Cosmetic surgery (e.g. a face-lift, liposuction)

Transmisogyny is generally understood to be caused by the social belief that men are superior to women. In "Whipping Girl", Julia Serano writes that the existence of trans women is seen as a threat to a "male-centered gender hierarchy, where it is assumed that men are better than women and that masculinity is superior to femininity". Gender theorist Judith Butler echoes this assumption, stating that the murder of transgender women is "an act of power, a way of re-asserting domination... killing establishes the killer as sovereign in the moment that he kills".

Trans women are also viewed as threatening the heterosexuality of cisgender men. In media, "deceivers" such as Dil, a transgender woman from the 1992 film "The Crying Game", have been observed to invoke outrage and male homophobia in an audience when their "true" maleness is unveiled.

A non-operative transsexual person, or non-op, is someone who has not had SRS, and does not intend to have it in the future. There can be various reasons for this, from the personal to the financial.

The word "transphobia" is a classical compound patterned on the term "homophobia", sharing its second component "-phobia" from the , "phóbos", "fear". The first component is the neo-classical prefix "trans-" from "transgender" (originally meaning "across, on the far side, beyond"). Along with "lesbophobia", "biphobia", "homophobia" and "transphobia" are members of the family of terms used when intolerance and discrimination is directed toward LGBT people.

"Transphobia" need not be a phobia as defined in clinical psychology (i.e., an anxiety disorder). Its meaning and use typically parallel those of "xenophobia".

The adjectival form "transphobic" describes things or qualities related to transphobia, and the noun "transphobe" denotes someone who harbors transphobia.

Although macrophilia literally translates to simply a "lover of large," in the context of a sexual fantasy, it is used to mean someone who is attracted to beings larger than themselves. Generally, the interest differs between people, and depends on gender and sexual orientation. They often enjoy feeling small and being abused, degraded, dominated, or eaten, and they may also view female giants as being powerful and dominating.

Commenting on why there are not as many female macrophiles, psychologist Helen Friedman theorized that because women in most societies already view men as dominant and powerful, there is no need for them to fantasize about it. Women that take on the roles of the giantess within this fetish often find the practice to be empowering and enjoy being worshipped.

The roots of macrophilia may lie in sexual arousal in childhood and early adolescence which is accidentally associated with giants, according to Dr. Mark Griffiths's speculation.