משנה על נזיר 51:6

[Blood] which was poured out in the air: If the place [where it fell] was an incline and [a person or vessel] overshadowed part of it, he [remains] clean. If it was a cavity, or if the blood congealed, he [becomes] unclean. If it was poured out on a threshold: If it inclined either inwards or outwards and the house overshadowed it [that which is in the house] is clean. If there was a cavity, or if it congealed, [that which is in the house becomes] unclean. Every part of a corpse is unclean except the teeth, hair and nails; But when they are joined [to the corpse], they are all unclean.