Mishnah Zavim 5:9: If one ate the carcass of a clean [kosher] bird and it is [still] in his gullet, he renders unclean at two [levels], and disqualifies [terumah] at one [level more]. [If] he stuck his head into the air-space of an oven [while the carcass it still in his gullet], it is clean [redundant words] and the oven is clean. [If] he spit it out or swallowed it, he renders unclean at one [level], and disqualifies [terumah] at one [level more]. But as long as it is [still] in his mouth until he swallows it, he is clean.

הָאוֹכֵל מִנִּבְלַת עוֹף טָהוֹר וְהִיא בְּבֵית הַבְּלִיעָה, מְטַמֵּא שְׁנַיִם וּפוֹסֵל אֶחָד. הִכְנִיס רֹאשׁוֹ לַאֲוִיר הַתַּנּוּר, טָהוֹר, וְטָהוֹר הַתַּנּוּר. הֱקִיאָהּ אוֹ בְלָעָהּ, מְטַמֵּא אֶחָד וּפוֹסֵל אֶחָד. וּכְשֶׁהִיא בְתוֹךְ פִּיו, עַד שֶׁיִּבְלָעֶנָּה, טָהוֹר:

Mishnah Zavim 5:10: One who touches a [dead] sheretz [ a creeping animal], or semen or has acquired corpse uncleanliness or a leper during his days of counting or the water [mixed with the ashes] of [the red heifer] sin offering of which there was insufficient for a sprinkling or the carcass of an animal or an object ridden upon, he renders unclean at one [level], and disqualifies [terumah] at one [level more]. This is the general principle, anyone who touches anything that according to the Torah is of primary uncleanliness renders unclean at one [level], and disqualifies [terumah] at one [level more], except [the corpse] of a human. If he separated himself [from the source of uncleanness], he renderds unclean at one [level] and renders unfit [terumah] at one [level more].

הַנּוֹגֵעַ בְּשֶׁרֶץ וּבְשִׁכְבַת זֶרַע, וּבִטְמֵא מֵת, וּבִמְצֹרָע בִּימֵי סָפְרוֹ, וּבְמֵי חַטָּאת שֶׁאֵין בָּהֶם כְּדֵי הַזָּיָה, וּבִנְבֵלָה, וּבְמֶרְכָּב, מְטַמֵּא אֶחָד וּפוֹסֵל אֶחָד. זֶה הַכְּלָל, כֹּל הַנּוֹגֵעַ בְּאַחַד מִכָּל אֲבוֹת הַטֻּמְאוֹת שֶׁבַּתּוֹרָה, מְטַמֵּא אֶחָד וּפוֹסֵל אֶחָד, חוּץ מִן הָאָדָם. פֵּרַשׁ, מְטַמֵּא אֶחָד וּפוֹסֵל אֶחָד: