I can't remember where I saw it (I hope it wasn't on here), but someone recommended that someone with vegetarian sympathies could do some good just by switching from chicken to beef. The idea is that if you're eating a constant amount of meat by weight, you have to kill a couple hundred chickens to get the same amount of meat as killing one cow. If you don't believe there's a significant "personhood" difference between cows and chickens, that's cutting your death toll by orders of magnitude.

I'm not sure what I think of this argument, because small differences in intelligence can have major differences in "personhood" - for example, I can't even name a number of cows it would take such that I would be equally comfortable killing X cows as one person. That means that even a small intelligence difference between cows and chickens could more than cancel out the gains from extra weight.

Really, what we need is some sort of animal which is both very large and very stupid. If only a stray prehistoric asteroid hadn't killed off our ideal food source.