We do not know when man first began to use salt, but we do know that it has been used in many different ways throughout history. Historical evidence shows, for example, that people who lived over 3,000 years ago ate salted fish. Thousands of years ago in Egypt, salt was used to preserve the dead. Because of its value as a preservative（防腐剂） , and flavoring, salt was considered, Romans and Hebrews it was a common sacrificial offering. Throughout the Middle East, moreover, it was a token（象征） of friendship and trust. Spilling such an honored substance was seen as an intentional offense to the celestial powers; the association of spilled salt with bad luck can therefore trace back to very ancient times. In Leonardo da Vinci's Last Supper, where Judas has knocked over the saltcellar（盐瓶） , the painter was mirroring an old tradition.

One many counteract the effect of spilled salt, or bad luck, by throwing a little over the left shoulder. The thrown salt may serve as an informal sacrifice to conciliate the gods; or it may be an attack on the evil spirits, since it is believed that the Devil cannot abide salt. It's the left shoulder probably because the right is associated with what is "right", but the left represents evil.