Psy Nail Bending -- Mentalism Magic

You borrow a nail. Mysteriously under impossible conditions, it bends itself in his hands. Once bent, he can't bend it back. Psy nail looks and feels like a standard nail but is indeed very special. Once you touch it, your body heat makes it bend. You'll either be able to add it secretly to a bunch of borrowed nail or switch it with a very common, similar type of nail.