This guy in my neighborhood when I was a kid used to bite his toenails. He'd grab an ankle and pull his foot up to his face, crane his head forward, clench the front of his teeth down on the corner of a nail and pull his head back taking a sliver of the nail with him. He would then look away and spit the shard into the air and then go down for another pass. I'm not embarrassed to admit that this is one of the coolest feats I've ever seen.