Or if a soul touch any unclean thing, whether it be a carcase of an unclean beast, or a carcase of unclean cattle, or the carcase of unclean creeping things, and if it be hidden from him; he also shall be unclean, and guilty.
If someone touches something dirty, like a dead animal or a dirty insect, even if they don't see it, they will become unclean and responsible for it.