[Regarding] a chicken that swallowed a sheretz and [then] fell into the airspace of an oven, [the oven] is tahor. But if [the chicken] died, [the oven] is tamei. [If] a sheretz was found in an oven, the bread that is in [the oven becomes] a sheni [l’tumah], for the oven is a starting [level of tumah].