 An additional factor is the type of interest in question. We can think of interests as scalar; crucial interests are weightier than important interests, important interests are weightier than replaceable interests, and all are weightier than trivial interests or mere whims. When there is a conflict of interests, crucial interests will always override important interests, important interests will always override replaceable interests, etc. So if an animal has an interest in not suffering, which is arguably a crucial interest, or at least an important one, and a person has an interest in eating that animal when there are other things to eat, meaning that interest is replaceable, then the animal has the stronger interest and it would be wrong to violate that interest by killing the animal for food if there is another source of food available.