As we learned, the Mishna (24a) distinguished between two cases when money was put aside for a nazir‘s sacrifices and then it turned out that there was no need to bring those sacrifices. For example, a woman accepted upon herself to be a nezira, and when her husband found out he was mefer – he nullified his wife’s vow. If the money was set aside for the sacrifices without specifying which money was for which korban, then the money should be used for voluntary olot sacrifices; if the money was set aside with specific sacrifices in mind, each of them should be used for a similar korban on a voluntary basis (i.e. not for the sacrifices of a nazir), except for the hatat – the sin offering – which must be destroyed.
Our Gemara gives the teaching in the name of Rav, as brought by Rav Huna, who claims that this distinction is true regarding money that was set aside. If, however, an animal was set aside then it will always be clear which sacrifice it is for.
The simplest explanation of this ruling is that since each of the different korbanot sacrificed by a nazir is brought from a different animal, we can know exactly which sacrifice the nazir had in mind: the hatat (sin-offering) is a female animal, the olah (burnt-offering) is a male and the shelamim (peace-offering) is a two year old ram. Thus if circumstances prevent the sacrifices from being brought at the end of the nezirut the hatat will be left to die, while the olah and shelamim will be brought as a voluntary olah and shelamim.
Tosafot argue that this cannot be the intention of Rav Huna in the name of Rav, since this ruling can be understood from the Mishna. Rather Tosafot suggest that we are dealing with a case where the animal that was set aside clearly cannot be brought as the korban of a nazir, e.g. he set aside several parim – cows – that cannot be brought as one of the sacrifices. The ruling is that we must see these animals as having been set aside to pay for all of the sacrifices, and since each of them includes a portion of the hatat sacrifice we will have to let these animals die – similar to the ruling that money set aside for a hatat that cannot be brought must be thrown into the Dead Sea.