I have double jointed thumbs. I can bend the top joint backwards as easily as forwards. When my doctor saw it, he was rather surprised. I never met anyone else who could do that until I worked at a piano store for a while. The manager, another pianist, and I were passing a bit of time on a slow day, and I told them I could do something they couldn't do, and bent both thumbs backwards in half. BOTH of them could do it! I was shocked. I can also raise my left eyebrow by itself-like Mr. Spock on Star Trek. What can you do?