<Li> In Brazil, "bater na madeira" (hit the wood) is something actually done physically, three knocks are required after giving an example of a bad thing eventually happening . No verbalization is required, just the three knocks on the closest piece or object of wood . In the absence of wood, someone can say "bate na madeira", to prevent the bad thing to happen . People do not actually believe knocking three times a piece of wood will really protect them, but it is a social habit and it is polite to do so to demonstrate that ones doesn't want that bad thing they are talking about to actually happen . </Li> <Li> In Greece the saying "χτύπα ξύλο" (literally: Knock wood) is said when hearing someone say something negative in order to prevent it from happening . </Li> <Li> In Lebanon and Syria the saying "دقّ عالخشب" (literally: Knock on the wood) is said when hearing someone say something negative in order to prevent it from happening . It is also largely observed when saying something positive or affirmative about someone or something and not wanting that to change . </Li> <Li> In Israel the saying "בלי עין הרע" (literally: without the evil eye) is said when someone mentions good things happening to themself or someone else, or even when mentioning a valuable things they own . This expression is a superstition that is used in the hope that a good thing will continue to occur even after it's mentioned, and as a way to prevent Envy (Hasad "حسد") also known as the Evil Eye (Ain Hara'a "عين"), as they believe that Envy can harm other people . </Li>

Where did the saying knock on wood come from