פירוש על ברכות 37:14

A portable earthenware oven is like an earthenware vessel and can contract defilement. In the latter instance, the vessel cannot be purified and must be broken to pieces. In the opinion of the Sages, the same rule applies to the oven. R. Eliezer allows the oven to be cut horizontally into layers and sand placed in between and cemented over.

Krauss, p. 251, thinks that the word translated "serpent" is really a proper name, Έχῖυοϛ, after whom that sort of oven was called. See his discussion in Part I of Lehnworter, pp. 295 f.