Professor Nobble was wearing a bucket upside-down on his head. It was a funny-looking bucket, and there were all sorts of things stuck onto it: pulleys and ropes, a rotating mouse-cage, a fork, and a mechanical hand holding a pen. "It's my thinking hat," the Professor explained. "It writes down whatever I'm thinking about, while I'm thinking about it. Here's how I make it go!"
Out of one coat pocket, he took a small white mouse; out of the other coat pocket, he took a piece of very smelly cheese. He put the mouse in the cage on top of the bucket. He put the cheese on the end of the fork next to the cage. When the mouse saw the cheese, its whiskers began to twitch and its legs began to run. The cage began spinning round faster and faster. The pen on the end of the mechanical arm began to move around.
"Now I need something to write on," said the Professor. He took a whistle from his pocket and blew it. Nobody heard anything, but an exercise book suddenly jumped out of the bookcase and began floating in mid-air in front of the Professor's nose. "It's another invention of mine," he said proudly. "Now all I have to do is think clearly . . . let's see . . . Let's all go to the Science Festival".
But something was terribly wrong: though Professor Nobble was thinking Let's all go to the Science Festival, all the pen would write was cheese cheese cheese cheese cheese . . . .