Every culture and country have their superstitions, and Japan is no exception. In fact, after spending a couple hundred years creating unique superstitions based on their own experiences and the animistic religion, Shintoism, they sent away to the mainland for a whole new set that came along with Buddhist culture. Then, when that wasn't enough, a bunch more were imported from the rest of the world. So, in addition to having to avoid the number 4 (the pronunciation is "shi" which is the word for death) and not sticking your o-hashi (chopsticks) into a bowl of rice, you also have to keep your eyes peeled for stray black cats. Staying lucky takes a lot of work.
One of my favorite superstitions is the admonition against whistling at night. Apparently it brings snakes runni...er...slithering. I read here that snakes is a metaphor for thieves. Considering how closely packed the houses are in Japan, it may have just been a convenient way to scare the kids into silence at night.