Baba Kama 115b - Bal Tashchis : בל תשחית

The gemara says that water that has been left uncovered and their is concern that snake venom may be inside, one cannot give the water to an animal. Rashi explains that the rationale is that we are concerned that one may shecht the animal and it will be dangerous to the person who eats from this animal. Tosafos points out that rashi's approach would only apply to a kosher animal, but in truth this din should apply to a non-kosher animal as well because there is a violation of ba'al tashchis to kill the animal for no reason at all. Tosafos proves this from a gemara in avoda zara 30b that it is only permitted to feed it to a cat (snake eater) which will not be damaged by the venom, which implies that it would be assur to feed it to a non-kosher animal which will be damaged by the venom. From Tosafos we see an interesting point regarding ba'al tashchis. Usually we refer to something as wasteful because it has a function to serve a human and it is being wasted. But in a case where the object provides no direct benefit to a human being one can argue that it is permitted to waste it without any violation of ba'al tashchis. Tosafos says that this is not true, because even a non-kosher animal similar to a cat that is not designated to assist people in carrying loads or plowing a field cannot be killed for no reason and would constitute a violation of ba'al tashchis.