There are many different versions of where the phrase “knock on wood” originated. The meaning is similar to warding off bad luck. It’s easy to research the origins but I won’t go into that here. Suffice to say this is not one of them. This is the Male Northern Flicker Woodpecker knocking on wood. Just a bit of trivia…Happy Wednesday.
My Precious Life 
That is the “yellow-shafted” variety; my neck of the woods has mostly the “red-shafted.” One of my favorite birds.
Thank you for your comments, Roger. They are appreciated. 🙂