>Is it only the dose?

I think they meant, for humans, the dose makes the poison. We would have to eat a very large amount of warfarin to have trouble. Rats get hurt from a small amount.

Poison is dose dependent, but the actual dose dependency is different between species.

I mean, however close we might treat them as, they're still fundamentally diferent animals

Since they can't throw up or burp, something that produces enough gas (More than a regular soda) could in theory kill a rat, but just make a human slightly inconvenienced, or on the same idea, you could wrap the poisson on an emetic agent to make it safer while not affecting the rat at all