And every earthen utensil, in which any of them falls, whatever is in it shall be unclean; and you shall break it (Lev. 11:33)
This shows, as is pointed out on our Talmud page, that this contamination – ritual impurity – follows over several levels:
R. Akiba lectured: And every earthen vessel, wherein any of them [sc. creeping things] falleth, whatsoever is in it shall be unclean [yitma]: it does not state tame [unclean] but yitma. [intimating that] it defiles [yetamme] others.
This intimation or hint is the basis for a whole range of levels of contamination – water from the vessel, for example, can contaminate food, which can contaminate other vessels, etc. to about the 4th level. This contamination is much discussed in rabbinic literature. Here is one example from our page:
Said R. Nahman b. Isaac, Come and hear: If a cow drinks the water of lustration (purifying liquid used in Temple ceremonies), its flesh is unclean. R. Judah said It [the water] is nullified in its bowels.
What purifies can also make unclean!
What does, ‘it is nullified in its bowels’ mean? It is indeed nullified from [imposing] grave uncleanness, but it does defile [with] light uncleanness. Hence it follows that the first Tanna holds that it is unclean even with the graver uncleanness; but surely he states, ‘Its flesh is unclean?’ The whole is R. Judah, but the text is defective, and it was thus taught: If a cow drinks the water of lustration, its flesh is unclean. When is that said? In respect of light uncleanness, but not in respect of grave uncleanness, for R. Judah maintained: It is nullified in its bowels. R. Ashi said: In truth it is completely nullified in its bowels, because it is [now] noisome liquid.