Polly Wants A Parrot

Polly Perkins was after a talking parrot, so she went to the local pet shop in the hope of securing such a find. She was in luck. The shop assistant assured her that the parrot would learn and repeat any word or phrase it heard. Polly was delighted. However, a week later, the parrot still hadn't spoken a word. Polly returned to the shop to complain, however, it appeared that the assistant was accurate in what he had said, and refused a refund. Why didn't the parrot talk?