I got this one by a book, but it's still fun.
While exploring the Amazon rainforest, Professor VanderSommen was seized by hostile natives. These natives told the professor that they were going to kill him unless he could solve his way out of the following problem.
The professor had a choice of how they would kill him. Here's how it worked: The professor had to say something. It could be and sentence that wasn't a question. If the professor made a false statement, he would be hit with a wet noodle until dead. If he made a true statement, he would be forced to drink prune juice until dead.
What is the only statement that Professor VanderSommen can make which will save his life?