What about if they bite their nails, all ten of them, and spit the bitten ends into their hand and hold them?
I've seen that on that subway. It's like watch a chimp in a cage at a zoo. I was mesmerized and then, when he was done carefully chewing each nail down to a respectable length, he sat there with his fist closed holding all of the bitten ends in his hand until he reached his destination.
I wondered: Did he just open his hand on the subway platform and let them scatter like seeds over newly turned soil? Did he wait until he passed the garbage can and then dump them in? I suppose not letting them fall over the floor of the subwar car was considerate, but does anyone need to watch someone bite down all their nails and know that those clippings of hard nails are jabbing at the inside of his hand for, oh, something like a half an hour!?