Research into great ape language has involved teaching chimpanzees, bonobos, gorillas and orangutans to communicate with humans and with each other using sign language, physical tokens, lexigrams, and mimicking human speech. Some primatologists argue that these primates' use of the communication tools indicates their ability to use "language", although this is not consistent with some definitions of that term. Apes that demonstrate understanding Non-human animals have been recorded to have produced behaviors that are consistent with meanings accorded to human sentence productions. (A production is a stream of lexemes with semantic content. A language is grammar and a set of lexemes. A sentence, or statement, is a stream of lexemes that obeys a grammar, with a beginning and an end.) Some animals in the following species can be said to "understand" (receive), and some can "apply" (produce) consistent, appropriate, grammatical streams of communication. David Premack and Jacques Vauclair have cited language research for the following animals (but see "Criticisms of primate language research", below): Chimpanzees Bonobos Gorillas Orangutans While communication appears to be a consistent feature utilized by all animals in the wild, the tendency toward autonomic behaviors and displays remains the most common among primates. Behaviors like body posture, facial expressions, vocalizations and scent production have been observed to convey information to other animals revealing emotions or alerts about potential danger. Behavior is also used to solidify hierarchical social rankings. In the natural world, affiliative behaviors such as grooming are used to promote group cohesion and relational status among primates. In contrast, displays of aggression can also create divisions among groups. Use of sign language Sign language and computer keyboards are used in primate language research because non-human primate vocal cords cannot close fully, and they have less control of the tongue and lower jaw. However, primates do possess the manual dexterity required for keyboard operation. Many researchers into animal language have presented the results of the studies described below as evidence of linguistic abilities in animals. Many of their conclusions have been disputed. It is now generally accepted that apes can learn to sign and are able to communicate with humans. However, it is disputed as to whether they can form syntax to manipulate such signs. Washoe Washoe, a common chimpanzee, was caught in the wild in 1966. When she was about ten months old, she was received by the husband-and-wife research team of Beatrix T. Gardner and