I volunteered at a no-kill shelter and only lasted a few weeks. Even though I knew none of the critters would get the "big shot" I just couldn't stand it (especially the dogs, when they bark and beg).

I used to work at an animal hospital, too. But the worste thing I ever saw were the owners who'd bring their pet in to be euthanised and not stay with them. Poor things would have to wait ALL day just to die.