Chickens are a type of bird, one of the most common and widespread domestic animals in the world.
In both the book and the movie, Mr. Krupp is hypnotized into believing he's a chicken. In both versions, Mr. Krupp begins clucking and flapping his arms. In the book, he jumps on his desk and kicks his papers back while pecking at his pen-and-pencil set. In the movie, he begins smiling and running around the room, his toupee standing upright to resemble a chicken's comb, before slamming his face into the floor repeatedly.