[If] one cut [the oven into] segments and placed sand between the segments, R’ Eliezer rules [it] tahor, but the Sages rule [it] tamei; this is the oven of the [coiled] serpent. Arabian cauldrons that one digs in the ground and plasters with clay: If the clay can stand on its own, it is tamei, but if not, it is tahor; and this is the oven of Ben Dinai.