Animal language
Animal languages are forms of non-human animal communication that show similarities to human language. Animals communicate through a variety of signs, such as sounds or movements. Signing among animals may be considered a form of language if the inventory of signs is large enough. 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 by chimpanzees and bonobos.