My stupid human trick is that I can flip my tongue all the way over. I don't know how uncommon it is; I do know that the extremely small sample size of people I asked -- my sister and Jeffrey -- can't. Heck, I didn't even know that I could do it myself until I caught myself in the mirror doing it sometime after college.
Well, turns out, Abbott does it, too. Also unknowingly, until I showed it to him in the mirror. Now he does it every night, looking straight at me. Like a little gang sign to me. He says, "Is this what you and I have together, Mom? We can flip our tongues over?"
I would never have been able to predict how much this delights me.