When I was building my shop.My nephew was holding some 2x4 while I was toe nailing.One of the 16 pennies shot right through the wood and penatrated his for arm at least 2 inches.The look on his face was priceless.Not to mention he jumped off a 10 foot ladder as soon as he seen it.
Strange as it seems, that happening isn't all that uncommon. When I had my stroke years ago my Neurologist was reassuring me I would be fine. He said "the brain is a very tough organ. I have patients who have nails imbedded in theirs and they don't even know they are there."