פירוש על שבועות 3:2

חייב על כל אחת ואחת – for since he stated, “bread” and “bread of each and every species,” one learns from it to allot/assign, for if it is to prohibit upon him these species and no others, he would have had to state, bread [made from] wheat, and similarly that of barley and that of spelt.

“I swear I shall not eat,” and he ate wheat bread, barley bread, and spelt bread, he is liable only once.
“I swear I shall not eat wheat bread, barley bread, and spelt bread,” and he ate [all three], he is liable for each one.
Mishnah two discusses a person who swears not to eat different types of bread. The question again is, how many different oaths did he make.
Similar to the end of the first mishnah, we learn here that if a person made one oath not to eat and did not specify what foods were covered, he will be obligated to bring only one sacrifice if he were to break the oath. If, however, he specifically swore not to eat three different types of bread and he ate all three, he is obligated to bring three sacrifices. In this case he has actually sworn three oaths and subsequently broken three oaths, thereby making him obligated for three sacrifices.