I'm getting the impression that monsters can sometimes use items in the space between me taking my turn and them dying. E.g. I fire a shotgun at a monster, taking it to -1/5 HP, but before it dies, it uses a medpack, bringing it back up to 1HP, and it survives. (I pulled those numbers out of thin air).
No real evidence for this - it's just based on too many experiences of former humans on the opening level surviving shotgun blasts to the face, and then healing, whereas I very, very rarely (if ever) experience them surviving such shotgun blasts and then NOT immediately healing. If you get my meaning.
If I'm correct in my suspicions, I think this rather unfair. After all, I don't have a chance to use my stockpiled medkits in a post-death capacity :P