Leviticus 5:2-3

2Or if someone touches any [ceremonially] unclean thing—whether the carcass of an unclean wild animal or the carcass of an unclean domestic animal or the carcass of unclean creeping things—even if he is unaware of it, he has become unclean, and he will be guilty.

3Or if he touches human uncleanness—whatever kind it may be—and he becomes unclean, but he is unaware of it, when he recognizes it, he will be guilty.