There are some strange superstitions w.r.t. death in Japanese culture. In Japanese the number 4 sounds sort of like death so it's a number they avoid a lot (it's missing from many elevator options, similar to how 13 is skipped sometimes) and patterns of squares are sometimes avoided to prevent having 4 corners meet (especially with straw mats).

I had never heard of this, though. The class of untouchables who work close to death. Really interesting stuff.