Did you know that the tradition of knocking on wood actually comes from the belief that every tree is inhabited by a spirit known as Hamadryad or Dryad? The action of knocking was practiced by ancient priests to immediately summon this spirit to aid the Priest or Priestess in order to ward off evil or fulfill a wish.
So the next time you knock on wood, remember that you are actually summoning the Spirit(s) of the Tree.
The Druids: Bringing in the Mistletoe
George Henry (1858–1943) and Edward Atkinson Hornel (1864–1933)