In the sanskrit texts that I have read about the interpretation of “mamsa” — it always refers exclusively to animal killing. It is different than the eating of fruit, which is an acceptable food and can be offered to God. Mamsa is seen as a sacrifice and a contract. Karma is not so direct in saying that that animal you eat will eat you as well specifically — but there is a connection of souls involved in the taking of a life. Buddhists will often say that every soul we know in our current life has played a role in all our other lives as well because karma brings familiar souls to each other again and again in various forms and roles. Killing is the same. I do believe that the killers of animals will take birth in animal form in their future births. This is talked about in the Vedas. Because the killing of animals is seen as sinful and results in a soul taking a lower birth. And because it’s only fair — which karma always is. Experiencing the perspective of the victim allows for a soul to develop empathy. I think this is why vegans may be more sensitive to the slaughter of animals than others — they have made sort of connection with the pain and fear of an animal because those feelings were emotions they had directly experienced. We have all existed in various life forms in countless lives — so being that we were all animals at many different points shouldn’t we feel more compassion for them as well? This is the purpose of re-births to put us in all different forms to show us that we are all just souls despite how we appear.