Eliza, as to poisoning mice and other animals eating the corpses,
think of the relative size of a dead mouse and the foraging cat.

Then think of the way mouse and rat poison works. It's warfarin (or maybe coumadin; I forget which is generic and which is the trademark name for human medicine).

The warfarin/coumadin slows blood clotting, and the mouse/rat dies of internal bleeding.

I don't know whether the warfarin/coumadin degrades in the rodent's metabolizing it. If it does, presumably it will have a lower level of effectiveness to the cat or dog which eats the cadaver. And even if it does not degrade and the cat or dog gets the full effect of what killed the mouse, that dose that killed the tiny mouse would have a much lower effect on the larger animal. Still might kill the scavenging cat/dog, but less likely, methinks.

By orders of my cardiologist, I take what I like to call "rat poison" (warfarin) every night before I go to bed.

Dave Oesterreich