Most research into the language capabilities of animals other than humans has used our closest relatives, which is why I was always particularly fascinated by Irene Pepperberg's work with Gray Parrots. Here's a quote from a wonderful article about her work:
"..we put a number of differently colored letters on the tray that we use, put the tray in front of Alex, and asked, "Alex, what sound is blue?" He answers, "Ssss." It was an "s", so we say "Good birdie" and he replies, "Want a nut."
Well, I don't want him sitting there using our limited amount of time to eat a nut, so I tell him to wait, and I ask, "What sound is green?" Alex answers, "Ssshh." He's right, it's "sh," and we go through the routine again: "Good parrot." "Want a nut." "Alex, wait. What sound is orange?" "ch." "Good bird!" "Want a nut." We're going on and on and Alex is clearly getting more and more frustrated. He finally gets very slitty-eyed and he looks at me and states, "Want a nut. Nnn, uh, tuh."
Isn't that wild?