Menahot 23: When Are Grain-offerings Not Like Animal Sacrifices?

Rava asks: If one takes a fistful of the grain and squeezes out the oil onto wood, does mean the fistful is missing its oil? Would that be invalid for an offering? How is that oil paralleled in animal sacrifice? (Or isn't it parallel?) Also, a new mishnah: Grain-offerings which haven't yet had the fistful taken from either one, and now the grain is mixed together - can they each have the fistful taken, or are they too blended? If the latter, then they're both invalid. The Gemara follows, with a dispute between Rav Hisda and Rabbi Hanina, regarding how meat that came to be in a mixture between impure meat and pure meat - when is the one kind negated or nullified in the other kind?