If two objects are presented to him and he's asked if they're the same or different, he will not only tell you if they are, but also in what way. Because different people work with the bird, there is no possibility that Alex is responding to unconscious visual cues coming from one teacher. They are learning to use words effectively as well, which proves that Alex's abilities aren't unique. With the advent of these behavior experiments, controversy has followed. Many people have a hard time accepting creatures other than man as having innate intelligence, due to their own fundamental religious beliefs.
Chimpanzees are physically unable to articulate words, no matter how diligently they are taught.
Washoe successfully used so many signs, that she was able to even compose short sentences and train other chomps. The gorilla baby, Koko, was even better at using sign language. Today, as an adult, Koko is still learning. The learning of songbirds has been studied in the laboratory, as well as in the wild. Amazingly enough, canaries were found to grow entirely new brain cells, every year, during their molt.