A professor invented a lie detecting chair. Whenever anybody sitting in it told a lie, the chair would open up and dump the liar on the floor.

During an experiment, a brunette sat in the chair and the professor asked her to tell about herself.

She began, "I think you are the best teacher I've ever had." The chair immediately dumped her on the floor.

After the brunette left in a snit, a blonde sat in the chair. The professor asked him to tell something of his life.

He began, "I think -"

The next thing he knew, he was sitting in the floor.