A somewhat interesting topic to ponder is if soap dirtiness. Since soap doesn't really kill bacteria, it can definitely be contaminated with bacteria such as E. Coli. Some studies go on to claim that infected soap is still just as effective at cleaning a person's hands (with no risk of contamination). Some even go on to claim that the water that's used doesn't necessarily have to be clean.
That's... I don't even know what to say.