Oh wow, that is interesting. I have said and written “knock on wood” many a time after mentioning an unpleasant thing that hasn’t happened, even in tweets with the character limit, and I do actually knock on wood every time. If I’m tweeting outside I often use the nearest tree. My friend from the Republic of Georgia will kinda spit over her shoulder three times, though it’s more like making a “puh” noise three times because no one wants to clean up spit. I don’t consider myself superstitious and I wouldn’t say she is either, but I guess there’s probably some psychological value. Especially if two cultures do basically the same thing in different ways to handle the issue of trying not to spend too much time or energy on imagining awful things.