Rashi states spleen and kidney are specified because removing part of them does not make the behamah a treifah. However on 55 A Rav Yosi Bar Zvidi tries to refute the position brought by Rav Avirah in the name of Rava that a nekav in the spleen makes the animal a treifah from our mishna which implies the animal is not a treifah. The gemorah in the first answer states really the animal is a treifah however since the raisha said moter b'achilah the safah said usser b'achilah. According to this answer why does our mishna specify spleen and kidney? Thanks,
Yehudah Relis
Yehudah Relis, Monsey NY
The Tosfos Yom Tov (4:1 DH "Min ha'Techol") indeed asks your question on Rashi and the Rav, and because of its severity gives a different explanation. He says that Techol and Kelayos are mentioned because it was normal (presumably semi-normal) to cut from the spleen and kidney when the animal was still alive. However, this question does not seem to me to be very difficult on Rashi using the rule of the Tosfos Rebbi Akiva Eiger on Mishnayos. Rebbi Akiva Eiger brushes away questions like this on Rashi by saying that Rashi did not necessarily explain the Mishnayos based on the conclusion of the Gemara, and will sometimes use an explanation which is only a "Hava Amina" (see i.e. Tosfos Rebbi Akiva Eiger on Shabbos 3:6). All the more so when there is another answer which does not mandate changing the simple explanation of the Gemara.
Kol Tuv,
Yaakov Montrose