Pesachim 47a, b

Shewbreads are the 12 loaves of bread that were placed on the sacred golden table in the Temple on Shabbat.  They were removed the following Shabbat and replaced.  Once removed, the loaves were to be eaten by the Priests.  Today's daf questions when it might be prohibited to bake or place or remove or eat those loaves.  The complications arise when Festivals 'interrupt' the Shabbat cycle.  The shewbread cannot be baked on Shabbat, and it cannot be baked on a Festival.  Thus sometimes bread might wait three days before being eaten, and at other times the bread might wait 11 days uneaten.  

The Gemara points out that on Shavuot, two leavened loaves are brought as a communal offering.  Additionally, two lambs were offered as a communal peace offering.  All of these were 'waved' and the loaves and lambs were divided and eaten among the priests.  Regarding this difference, the Gemara reminds us that Exodus 12:16 tells us "No kind of labour shall be done on them save that which every man must eat, that only may be done for you".  "You" refers to human consumption, as opposed to for G-d, ie. the Temple service.

This is used to argue whether or not baking the shewbread overrides Festival prohibitions.  Rav Chisda then brings in a case where eight prohibitions are transgressed with one act.  First, the ox must not plow with the donkey, second, they were consecrated, third, they helped to grow food crops in a vinyard, third & fourth, it is a Sabbatical year and a Festival, next, it is a priest and a nazirite plowing a ritually impure place (graveyard).  But if the plowing covers the blood of a killed bird, as required, -- he should not be liable for plowing (a positive Torah commandment overrides the prohibition of labour on a Festival, which is a rabbinical law).  The rabbis argue about contingencies which might mitigate the ruling in this case: was the soil rocky? crushed up? muddy? 

Into daf (b), the rabbis look at a similar case.  One who cooks the sciatic nerve in milk on a Festival and eats it is flogged for five prohibitions.  In a note, Steinsaltz explains that this was in fact overruled as halacha, for the sciatic nerve is not considered to be tasty like meat.  The rabbis argue about which laws have been transgressed.  They then look at whether or not a found lamb can be used as a daily offering on a Festival.  We would have to know that the lamb is one of two hundred, not a first born, not an adolescent (between 365 days and 395 days), and not one of a group of ten.

I find myself (as usual) oscillating between reverence for the care put into the laws around offerings and exhaustion at the detailed analysis of every possible legal path.  Whenever animals are involved in the conversation, I perk up.  Even when those animals are about to be killed.   The debates over language, grammar, principles and other 'rules' are equally engaging and off-putting.