Hullin, Chapter Six, Mishnah Five
Our mishnah deals with blood that comes out of a slaughtered bird or wild animal that then becomes mixed up with something else, either water, wine or blood.
1) If the blood became mixed with water and it still has the color of blood, it must be covered up.
2) If it became mixed with wine, [the wine] is to be regarded as though it was water.
3) If it became mixed with the blood of a beast or with the blood of a wild animal, it is to be regarded as though it was water.
a) Rabbi Judah says: blood does not annul other blood.
Section one: If the blood becomes so mixed up with water, that it no longer has reddish color, then it is no longer considered to be blood and it need not be covered up. But if it still has the color of blood, it must be covered, despite the fact that there is water mixed in.
Section two: Wine has the same color, more or less, as blood, so we cant say that if the mixture has the color of blood then it must be covered up. Therefore, if there is enough wine such that if it was water there would no longer be the color of blood, then he need not cover it up. This is what it means when the mishnah states that the wine is regarded as water.
Section three: The blood of a domesticated beast (cow, sheep or goat) need not be covered. If the blood of a wild animal or bird is mixed up with the blood of a beast, then we apply the same test as we did with blood that was mixed with wine. If there is enough wild animal or bird blood such that if the beasts blood was water the mixture would still look like blood, then he must cover it up.
This section has some very puzzling wordsor with the blood of a wild animal. The blood of a wild animal must be covered and therefore this line makes no sense in this context. Albeck suggests that it is here by mistake, due to the similarity between this mishnah and Zevahim 8:6 where the words the blood of a wild animal do make sense. Rashi suggests that the blood of the wild animal came out not by slaughtering, while the Rambam suggests that the wild animal referred to here is not a kosher one. Neither suggestion is convincing.
Rabbi Judah says that blood can never annul the presence of other blood. While an overwhelming amount of wine or water could exempt a small amount of blood from having to be covered, the same cannot be said about blood. In general, Rabbi Judah holds that when two like things are mixed, the problematic thing (for instance nevelah meat mixed in with kosher meat) can never be annulled.