Why didn't they just use cats??
Because cats just sit around all day on their fat asses, and can't be bothered with doing anything, until they turn up their noses at the can of tuna fish that you opened.
Some cats. Not my cat. He has no front claws, is a town cat that I Iet roam at night, and drops in my driveway from 1 to 3 mice most nights. He only caught about 3 birds all summer, but he also caught and killed about a half dozen rabbits. They were cottontails, and not full grown but the last couple he caught in September where getting close to full sized. Does he kill things that he doesn't bring back? Who knows, but I think I get to see most of his work. His brother is a farm cat, and regularly catches gophers and brings them to the farm house.