An idioglossia is an idiosyncratic language invented and spoken by only one person or very few people. Most often, idioglossia refers to the "private languages" of young children, especially twins, the latter being more specifically known as cryptophasia, and commonly referred to as twin talk or twin speech.
Children who are exposed to multiple languages from birth are also inclined to create idioglossias, but these languages usually disappear at a relatively early age, giving way to use of one or more of the languages introduced.
Sam and Ren McEntee, 17-month-old twins.
June and Jennifer Gibbons
Kennedy twins of San Diego, California, who were subjected to intensive study, including an exhaustive analysis of their language. (They named themselves "Poto and Cabengo")
The 1994 film Nell, starring Jodie Foster, depicts a woman who speaks an idioglossia. The stage play on which it is based is also called Idioglossia.
The concept album The Perfect Element, part I, by Pain of Salvation, is centered on a song titled "Idioglossia".
James Joyce's novel Finnegans Wake was written using an idioglossia.
Skins Series 3 Episode 9 shows Katie and Emily Fitch using an idioglossia.
Sherri and Terri on The Simpsons sometimes use an idioglossia.
The two teenage protagonists of the film Disco Pigs, Darren and Sinéad, use an idioglossia.
Singer, musician, and composer Lisa Gerrard (of Dead Can Dance and in her solo career) sings many of her songs in an idioglossia that she has developed since the age of twelve.
A Bug's Life (1998) – Tuck and Roll.
The twin brothers Jim and Tim Possible from the Disney Channel series Kim Possible often use twinspeak.
Twins Marilyn and Carolyn Arnold from The Baby-Sitters Club book series used this early on.
In the 2005 Law & Order: SVU episode "Identity", teenage twins Logan and Lindsay Stanton (Reiley McClendon) speak to each other in twin language while both are being interrogated in a murder investigation by Detectives Stabler and Benson (Christopher Meloni and Mariska Hargitay, respectively). Detective Stabler recognizes their language as "twin speak" because he himself is the father of twins and remarks that his twins had their own language when they were young as well.
In the 2010 American Dad! episode "Son of Stan", Steve and his temporarily created clone, Steve-arino (voice of Scott Grimes), were briefly seen using an idioglossia in speaking to each other.
In episode 212 of television show Rules of Engagement, twins attending a party speak in twin language and state that twins often have their own language that only they can understand.
The popular YouTube video Talking Twin Babies
The television series Second Chance have twin sister and brother Mary and Otto Goodwin who sometimes use twin speak to communicate with each other.
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