2,907. Not Every Form of Corpse Impurity

Hilchos Nezirus 6:20

Let’s say that a nazir who was rendered unclean by a corpse went into a cave and immersed there. He brings his impurity offering, counts the days of his nezirus, and shaves in purity, after which he learns that there was a corpse sunken in the ground of the cave when he immersed. Even though this was an unknown impurity, all the days of his nezirus are voided because, in this case, he was already established to be unclean. He maintains a presumption of ritual impurity until he is definitely purified. If a nazir went into the cave to cool off, he remains ritually clean until he knows for sure that he touched the body (because he maintains his presumption of ritual purity until there’s good reason to believe otherwise). If the body is found floating on the water, then we assume that he’s unclean. Since the body is floating, we presume that the nazir most likely touched it.

Hilchos Nezirus 7:1

Some types of corpse impurity don’t require a nazir to shave, nor do they cancel out the days he already observed; this is so even though he must observe seven days of impurity. This is because the Torah doesn’t say the rule applies just because he was rendered unclean through corpse impurity. Rather, Numbers 6:9 specifies that the rule applies “when a person dies on him.” This means only when the nazir is rendered unclean via the actual deceased. He must then bring the offerings and shave for impurity. All the days of his nezirus until that point are voided.