I think we have all said "knock on wood" before after bragging that we have done this or that and had no problems. It's just an expression for me and I never really think about truly knocking on wood. Some superstitious types take the saying literally and need to have some wood around to knock on.
If you are one of these sorts, some new stickers for your iPhone and other gear have surfaced that are actually made from wood. The stickers are Torchwood Stickers and have self-adhesive goo on the back to stick them to your gadget.
The stickers come in a pack of three real wood stickers. One of the stickers is a circle, one is a square, and one is a rectangle. The stickers can be ordered right now for £5.00 or roughly $8 in the US. They come from a company called Suck UK.