it cant just appear on a clock face, unless you set up the gimmick...
hopefully i wont get banned for exposure, but he has a large invisible thread reall attached to the back of the clock, and when he rips off the piece, he attaches it with misdirection, and then just after he shows the piece, the piece is let go and flies onto the clock hand, piercing itself...
the reason the flying corner isn't seen is due to the fact that he sneezes very loudly when letting go, for distraction purpose, and the camera cuts at this point, to not show you the whole effect!
pretty simple when you think about it