What sickens me is when the "winner" who actually makes it to the bonus round doesn't solve the last puzzle and loses the $100K prize. Once Pat opens up the envelope and closes it quickly, you know what the player lost. This happens from time to time.
On another note, what I like about WoF is when one of the contestants incorrectly "solves" the puzzle, Pat replies "That is not correct, I'm so sorry" or the like.