Is the occasion to need to put down sick critters sometimes. Yesterday it was the kids favorite little goat. It contracted Tetanus after we banded him, despite taking medicinal precautions. I gave him a couple shots to treat the condition but once it takes hold it is most often fatal. I found him stiff as a board, not able to open it's moth and in shock.
Last time I had to do this I took occasion to try out my little pocket .380 with Hornady 60 gr. Critical Defense JHP ammo. The $2 a round stuff I carry often. VERY unimpressed. I had to shoot it twice! Just poked a 9mm hole in and out. But I've never been impressed with .38 S&W which is a like performer.
This time I used my carry "pocket" .45 ACP which happened to have a rogue left over 185 gr. JHP. I've taken to carrying ball these days, for reliability and penetration. No telling what I might be called to shoot around the place. (like a sick horse once) It was perfect and humane, instant relief for the poor beast. Exit side was a little messy but expected. Use enough gun. My .40 with FN cast 200's would have been fine too, just didn't think of it.