A talking animal or speaking animal is any non-human animal that can produce sounds or gestures resembling those of a human language. Several species or groups of animals have developed forms of communication which superficially resemble verbal language, however, these are not defined as language because they lack one or more of the defining characteristics, i.e. grammar, syntax, recursion and displacement. Researchers have been successful in teaching some animals to make gestures similar to sign language. However, these animals fail to reach one or more of the criteria accepted as defining language.