Yoma, Chapter Eight, Mishnah Three
This mishnah deals with how many sin-offerings one would be liable for if he ate or drank on Yom Kippur. The sin-offering is the sacrifice brought for an inadvertent sin. We have seen a similar type of mishnah in the beginning of the seventh chapter of Shabbat. As I might have explained there, this is the way that the rabbis define just how many sins a person has committed.
1) If he ate and drank in one state of unawareness, he is not obligated to bring more than one sin-offering.
2) But if he ate and performed labor while in one state of unawareness he is obligated for two sin-offerings.
3) If he ate foods unfit for eating, or drank liquids unfit for drinking, or drank fish-brine or fish pickling liquid, he is not liable.
Section one: If a person didnt know that the day was Yom Kippur or he didnt know that it was prohibited to eat or drink on Yom Kippur and he ate or drank many times during the day, he is only liable for one sin-offering. This is one sin, since eating and drinking are two aspects of the same prohibitionsthe commandment to afflict oneself on Yom Kippur.
Section two: Eating/drinking and performing labor are two different prohibitions. Therefore if someone does both on Yom Kippur, even in one state of unawareness (for instance, not knowing that it is Yom Kippur) he is still liable for two sin-offerings.
Section three: In order to be liable for eating or drinking, that which one eats must be food that is fit for eating or liquid that is fit for drinking. Otherwise, one is not liable. Note, the mishnah does not say that one is allowed to do so, just that doing so does not incur liability for transgressing a Torah law. It is still prohibited.