Cats are great for that, until they leave prizes on your pillow. Now that was a sick & twisted kitty. Guess it was intended as my
cut as boss of the house. The (ex)girlfriend was not pleased to find one nearly in her ear.
Then there's the risk of an impotent cat. My sister has one that apparently thinks his gaze is enough to kill. It will watch mice and sort of squint then go wide-eyed then squint again. Never doing more than shifting its body to keep the mouse in sight until actual exertion would be required. Then he goes inside to eat and watch the TV. I call him Gort.
Anyway, yes I felt bad after killing Mickey & Minnie. It was distressing to be working, hear the *SNAP* and actually see one perish. The part about feeling ill wasn't far from the mark.