Animal languages are forms of non-human
animal communication that show similarities to human
language. Animals communicate by using a variety of signs such as sounds or movements. Such signing may be considered complex enough to be called a form of language if the inventory of signs is large, the signs are relatively arbitrary, and the animals seem to produce them with a degree of volition (as opposed to relatively automatic conditioned behaviors or unconditioned instincts, usually including facial expressions). In experimental tests, animal communication may also be evidenced through the use of
lexigrams (as used by
chimpanzees and
bonobos). While the term "animal language" is widely used, researchers agree that animal languages are not as complex or expressive as human language.