Keilim9: 3
[ג] הַשֶּׁרֶץ שֶׁנִּמְצָא לְמַטָּה מִנְּחֻשְׁתּוֹ שֶׁל תַּנּוּר — טָהוֹר, שֶׁאֲנִי אוֹמֵר: חַי נָפַל וְעַכְשָׁיו מֵת. מַחַט אוֹ טַבַּעַת שֶׁנִּמְצְאוּ לְמַטָּה מִנְּחֻשְׁתּוֹ שֶׁל תַּנּוּר — טָהוֹר, שֶׁאֲנִי אוֹמֵר: שָׁם הָיוּ עַד שֶׁלֹּא בָא הַתַּנּוּר. נִמְצְאוּ בְאֵפֶר מִקְלֶה — טָמֵא, שֶׁאֵין לוֹ בַּמֶּה יִתְלֶה.
[Regarding] a sheretz that was found beneath the floor of an oven, [the oven is] tahor, for I say: It fell while alive and [only] now did it die. [Regarding] a needle or ring that was found beneath the floor of an oven, [the oven is] tahor, for I say: They were there before the oven arrived. [If] they were found in the ashes, [the oven is] tamei, for there is nothing to which it can be attributed.
Keilim9: 4
[ד] סְפוֹג שֶׁבָּלַע מַשְׁקִין טְמֵאִין וְנָגוּב מִבַּחוּץ, וְנָפַל לַאֲוִיר הַתַּנּוּר — טָמֵא, שֶׁסּוֹף מַשְׁקֶה לָצֵאת. וְכֵן חֲתִיכָה שֶׁל לֶפֶת וְשֶׁל גֶּמִי. רַבִּי שִׁמְעוֹן מְטַהֵר בִּשְׁנֵי אֵלּוּ.
[Regarding] a sponge that absorbed tamei beverages and was dry on the outside and it fell into the airspace of an oven, [the oven is] tamei, because the beverage will eventually emerge. And similarly a piece of turnip or of reed-grass. R’ Shimon rules tahor in these two [cases].