Abaye proved that a animal is not tamei even masa inside the throat. Why couldn't Rava push back that it would be tamei masa inside the throat, it's only excluded from metama clothes? Based on learning that Abayeis proof was from animal not bird - the way V'Shinantam print of gmara explains.
Daniel Gray, Toronto Canada
1) The tuma of masa occurs when a person carries a tamei object. This makes the person carrying it tamei, even if he did not actually touch it (because if he touched it he would become tamei maga).
2) The tuma of the neveila of a pure bird is a special tumah. See Rashi Vayikra 22:8 that this does not possess tuma of maga or masa. The only tumah that it has is that when the neveila of the pure bird is in the throat it makes tamei any clothes which one is wearing, or any keilim one touches (see Rambam Avot Hatumot 3:1).
So tamei masa is not applicable inside the throat. He would be tamei maga there since his throat touched the tuma.
Good Shabbos
Dovid Bloom