According to the Mishnah on yesterday’s daf (=page) a person can eat a single olive-size bit of meat and be liable for four separate sin-offerings (hatat) as well as a guilt-offering (asham). The case would be if the person was ritually defiled and he ate:
Helev (forbidden fat) that was notar (it was left over from a sacrifice past the time that it could be eaten), so it was from an animal that was sanctified for the altar, on Yom Kippur. This person would be obligated to bring separate sin-offerings
1. for eating forbidden fats
2. for eating meat from a sacrifice after the time that it was permitted
3. for eating sanctified meat while ritually defiled, and
4. for eating on Yom Kippur.
He is also obligated to bring a guilt-offering for having taken from the sanctified animal (me’ilah).
Rabbi Me’ir adds that if it was Shabbat and he walked into the public domain with the meat in his mouth, he would be obligated to bring a fifth sin-offering, for carrying in the public domain on Shabbat.
Today’s daf opens with a question: This appears to be a case of issur hal al issur – that the prohibitions are being piled one upon the other – and Rabbi Me’ir rejects such a possibility! (The Ramban explains that the assumption of the Gemarais that the entire anonymous Mishnah is the opinion of Rabbi Me’ir.) In response the Gemara explains that although Rabbi Me’ir does not believe that issur hal al issur, nevertheless he does accept the idea of issur mosif – that when the new prohibition has an added element of prohibition, it can be added to the existing prohibition.
In our case, the basic prohibition is that it is forbidden to eat the forbidden fat. Once it was sanctified, it became forbidden to derive any benefit from that meat. When the man became ritually defiled he cannot eat any sanctified meat. Finally, when the meat became “left over” it became forbidden to all. Since each of these includes more than the previous prohibition, all of the prohibitions take effect.