The Thurber & White send-up on the knee phenomenon:

Simply stated, the knee phenomenon is this: occasions arise sometimes when a girl presses her knee, ever so gently, against the knee of the young man she is out with… Often the topic of conversation has something to do with it: the young people, talking along pleasantly, will suddenly experience a sensation of compatibility, or of friendliness, or of pity, or of community-of-interests. One of them will make a remark singularly agreeable to the other person—a chance word or phrase that seems to establish a bond between them. Such a remark can cause the knee of the girl to be placed against the knee of the young man. Or, if the two people are in a cab, the turning of a sharp corner will do it. In canoes, the wash from a larger vessel will bring it about. In restaurants and dining-rooms it often takes place under the table, as though by accident. On divans, sofas, settees, couches, davenports, and the like, the slight twist of the young lady’s body incident to receiving a light for her cigarette will cause it… Now, a normal male in whom there are no traces of frigidity will allow his knee to retain its original position, sometimes even exerting a very slight counter-pressure. A frigid male, however, will move is knee away at the first suggestion of contact, denying himself the electric stimulus of love’s first stirring.