One of the most common stylistic elements found in the Gemara is that the Gemara first brings a Mishnah in its entirety and then quotes short snippets from that Mishnah and discusses them at length. Occasionally, after the Gemara quotes a baraita, it chooses to examine the baraita in the manner that it usually analyzes a Mishnah, and we find a similar method of short quotes followed by lengthier explanations.
On today’s daf (=page) we find that the Gemara brings the following quote: “…and one who slaughters them outside of the Temple precincts is not culpable.” In this case we find disagreement as to the source of this quote, since our Mishnah (above, daf 14a) reads that someone who slaughters a blemished animal outside of the Temple precincts is, in fact, culpable.
Rashi suggests that the source of the quote is not the Mishnah, but the baraita that was brought earlier, which is dealing with the case of an animal that was sanctified after it was already blemished. In that case the animal never receives intrinsic holiness and its slaughter outside the Temple precincts is not a problem.
From the Rambam it appears that this is a quote from the Mishnah and that according to his manuscript of the Mishnah even someone who slaughters an animal that became blemished after it was sanctified outside of the Temple precincts is not culpable. According to this reading, the version that appears in our Mishnah is a “correction” based on Rav Huna‘s teaching in the Gemara. For the Gemara quotes Rav Huna as reading in the Mishnah “He is culpable.” He explains it as relating to a specific case where the blemished animal was suffering from dukin she-ba’ayin in accordance with the opinion of Rabbi Akiva who permits certain types of mumim to be brought on the altar (or at least that the sacrifice is not removed from the altar if it had already been brought to it).
Dukin she-ba-ayin is some kind of an eye condition; Rashi explains that it is a cataract on the eye. Another possible explanation presented by Rashi is that it is a blemish on the eyelid. Since dukin she-ba-ayin is a relatively minor condition – in fact, it is not considered a blemish if it is found in a sacrifice brought from fowl – Rabbi Akiva rules that an animal with such a blemish is permitted if it found its way to the altar.