What is "pull my finger"

vb. A phrase used when playing a prank regarding flatulence, in which a mark is asked to pull the finger of the person playing the prank, who simultaneously flatulates so as to suggest a causal relationship between the pulling of the finger and the resulting expulsion of gas.

Pull my finger is a joke or prank regarding flatulence in which a mark is asked to pull the finger of the joker, who simultaneously expresses gas (aka farts) in an unsavoury fashion so as to suggest a causal relationship between the pulling of the finger and the subsequent expulsion of gas.

A comparable activity is attributed to a character in a short story by Mordecai Richler (collected in The Street, 1969):

A variation on this joke appears in Yasujiro Ozu's film Good Morning ( 1959). Schoolboys ask each other to push their foreheads, responding with an expulsion of gas.

In 2008, an iPhone app from Air-O-Matic called Pull My Finger was one of the most popular apps in Apple's App Store, purchased over 50,000 times in less than one week. It allowed users to pull a virtual finger, activating the sound. The phrase is now the focus of a legal battle between Pull My Finger and InfoMedia's iFart Mobile app over the use of the phrase.

In 2015, an MRI study of how knuckles trigger popping sounds were jokingly called the "pull my finger study."