Hullin, Chapter Two, Mishnah Five
In order for food to become susceptible to impurity it must come into contact with one of seven liquids (see Leviticus 11:38). When an animal is slaughtered, assumedly blood will come out and render the meat susceptible to impurity. Our mishnah discusses a situation where an animal is slaughtered and blood does not come out.
1) If one slaughtered cattle or a wild beast or a bird and no blood came out, they are valid and may be eaten by him whose hands have not been washed, for they have not been rendered susceptible to impurity by blood.
2) Rabbi Shimon says: they have been rendered susceptible to impurity by the slaughtering.
Section one: Although blood did not come out of the animal (be it wild or domesticated) or the bird, the animal can still be eaten. We dont assume that the animal was already dead when it was slaughtered and therefore no blood came out. We also dont prohibit the animal because of the blood inside the animal, because blood that is inside an animal is not prohibited.
Since the meat cannot receive impurity, one who has impure hands because he has not washed them can eat the meat without fear of causing it to be impure. This would have important ramifications if the animal was sacred and was being eaten by priests. Alternatively, it would have ramifications if the person simply desired to eat his meat in a state of purity.
Section two: Rabbi Shimon says that the very act of slaughtering renders the animal susceptible to impurity. Since the slaughtering causes the animal to become permitted for eating, it also causes the animal to become susceptible to impurity.