Leviticus 5:2-3

2Or when there is a person who touches anything ceremonially unclean, whether the carcass of an unclean wild animal, or the carcass of an unclean domesticated animal, or the carcass of an unclean creeping thing, even if he did not realize it, but he himself has become unclean and is guilty;

3or when he touches human uncleanness with regard to anything by which he can become unclean, even if he did not realize it, but he himself has later come to know it and is guilty;