Since ancient times, one's spittle has been valued as a charm against all evil. Spitting is a way of consecrating or anointing. To spit on anything has been accepted as a method of ensuring good luck or success in an undertaking for so long that no one can determine when the practice began.
Sailors spit on their ships for luck. Fishermen spit over the edge of their boats to guarantee a good catch. Schoolboys spit on their shooter marbles for luck in knocking the other players' marbles out of the circle. In the old days, those about to engage in a fistfight spit on their knuckles to increase the power of their blows. Even today, some people who are about to undertake a difficult physical task first spit on their hands to make the job easier.
In many cultures, if people accidentally drop their money, they must spit on it for luck after they retrieve it. Others spit on their money for luck before placing a bet on a sporting event. Some individuals spit on their paycheck to bless it before cashing it. Modern postal employees are used to seeing people spit on the envelopes containing contest entries before the hopeful contestants drop them in the mail slot.
Almost universally, if people feel that a person with evil intent has put the evil eye on them, they must spit immediately to protect themselves from the curse. Whenever individuals sense that a spell of witchcraft for sorcery has been directed toward them, they must spit over their left shoulder. If one should awaken from a frightening nightmare, one must spit over the left shoulder three times to be certain that it doesn't come true. Even if one should encounter Satan himself, the Prince of Darkness can be made to disappear if one spits between his horns.
In the gospel accounts of the ministry of Jesus (c. 6 B.C.E.–c. 30 C.E.), the miracle worker from Nazareth healed people of blindness and deafness with his spittle. The ancient Greeks believed that eye troubles could be cured by rubbing them with the spit of someone who had been fasting. On occasion, mothers worldwide use their spittle to rub over their child's bruise or cut to make it heal faster.