My sister has double-jointed thumbs. She can bend them right back and touch her forearm. I can't, but once by accident my thumb got bent back like that, with minimal pressure. It was the most painful experience of my life. I actually lost all vision and I saw nothing but red for the instant that my thumb was bent the way my sister can bend her thumbs easily.
Genetics. Is there nothing it can't do?
\went straight to the freezer and packed my hand in ice
\\no permanent damage, unlike almost every other joint in my body
\\\getting old sucks. Be careful while you're young. Stuff doesn't heal