This is a story about my brother-in-law (we'll call him Bruce).
Bruce is an identical triplet and has always been amazingly cool. He and his brothers had to have the sturdiest cribs available because they would stand up in them and throw their body weight around, using them as makeshift bumper cars.
When Bruce was little, his parents noticed that every once in a while, he would rapidly jerk his head from side to side. Usually, it was when he watched TV.
They were understandably concerned and took him to a specialist to find out what was wrong. When none of the tests identified anything, they took him to another specialist. He went through several doctors who were all baffled at what could be the problem.
Finally, one doctor sat down next to Bruce and asked, "Bruce? Why to you jerk your head back and forth?"
Bruce said, "Oh, that? I like the way my hair feels when it brushes against my forehead."