Sucking is a rhythmic motion, and the stronger the suck, the more it palpates the roof of the mouth. As the roof of the mouth rises and falls, the sphenoid bone lifts. This bone is shaped like a butterfly, with wings that reach out to the temples and a body that rests on the back of the skull. When the sphenoid lifts, dopamine flows. Dopamine is a hormone that makes us happy. It’s one big reason kids like to suck their thumbs – it activates the sphenoid, that dispenser of good-feelings.