Out of the experiments discussed in the book, the one discussed in Facing the Uncanny Valley. Relating to how covert reactions can determine your own emotions, the imagined experiment discussed how holding a pen in between your teeth would correlate to you rating cartoons as funnier than if you were holding the pen with your lips or just in your hand.
This is because when holding the pen with your teeth, you are sort of activating the muscles in your face used to smile. Your facial expression when holding the pen with your teeth could subliminally cause you to be in a happier state, even if you are not purposely smiling or even aware you are doing it.
If you're ever having a bad day, walk around with a pen between your teeth for a while! It may subtly boost your mood.