A sneer is a facial expression of scorn or disgust characterized by a slight raising of one corner of the upper lip, known also as curling the lip or turning up the nose.[1] In The Expression of Emotions in Man and Animals, Charles Darwin defined a "sneer" as "the upper lip being retracted in such a manner that the canine tooth on one side of the face alone is shown"[2] Darwin related the sneer to the snarl observed in non-human animals, particularly carnivores, observing that:
It is suggested that the sneer is a universal expression of contempt[4] and that Darwin was the first to observe this.[5] Cats may be observed to sneer, though this is probably related to the Flehmen response.[6]