Sometimes the categories animal, vegetable, and mineral are used instead of person, place and thing. The guessers have 20 questions, and if they do not get the correct answer before they run out, the Answerer ('It') wins. Usually if a guesser figures out what 'It' was thinking of, they in turn become It.
This whole thing is more fun if you get unlimited questions and can use anything from any category (things such as 'light', 'numbers', and 'HAL' don't fit well into the traditional three categories). A very good geek game. When you get bored with 20 questions, move on to Questions.