Well you see, the play clock has to hit zero. The referee has to look at his watch to confirm the zero. He then has to look at the ball. Then he has to look back up at the play clock to make sure that the first zero wasn’t a mirage. Then back down to his watch to make sure there are no glitches in the Matrix. Then back up to the ball. If is still not snapped, he/she then the makes the call.