The orangutan Azy selects a symbol for "apple" after being shown a slice of apple by a researcher at the Think Tank facility at Washington, D.C.'s National Zoo in 1996.
"Not only does Azy communicate his thoughts with abstract keyboard symbols, he also demonstrates a 'theory of mind' (understanding another individual's perspective) and makes logical, thoughtful choices that show a mental flexibility some chimpanzees lack," according to National Geographic magazine.
As part of the facility's Orangutan Language Project, orangutans, rewarded with food, learn to use a symbol-based language presented on a computer monitor, according to the Think Tank website.
The zoo's "dictionary" has about 70 abstract symbols, all of which have no visual relation to the object they represent. There are seven categories of symbols: food, proper names of people, verbs, adjectives, Arabic numbers, nonfood objects, and proper names of orangutans.
Though it wasn't the first time an ape had commuicated via symbols, Azy's accomplishment "meant a nonhuman species could attribute meaning to otherwise meaningless arbitrary symbols," Russon said.
(Related: "Orangutans Show Signs of Culture, Study Says.")