A gesture that takes a second and encodes a doctrine. Three fingers joined for the Trinity with two folded against the palm for the two natures of Christ is the Eastern form; the West uses an open hand and crosses left to right rather than right to left, a divergence nobody planned. It is done on entering a church, passing one, before eating, before a journey, at the mention of the dead, and by footballers before a penalty. The Russian schism of the seventeenth century turned on exactly this: Patriarch Nikon's reforms changed the sign from two fingers to three, and the Old Believers who refused were persecuted for centuries, some burning themselves in their churches rather than conform. It is a good corrective to the idea that small ritual details are trivial to the people who keep them.