In a game governed by a complex set of unwritten rules, there is perhaps none more sacred than silence. A no-hitters is an uncommon sight, and perfect games are even rarer still (only 20 have been thrown so far). So when a pitcher is en route to either of these extraordinary feats, teammates take a vow of silence to not mention the no-hit or perfect game bid for fear of jinxing the pitcher. Practically speaking, this allows the pitcher to maintain whatever rhythm he has going, rather than needlessly dwelling on the probabilities of the gargantuan task at hand.