When you hear the phrase "working animal" it probably conjurers up visions of either horses on a cattle drive or seeing eye dogs. We mostly think about dogs or horses doing the majority of "work" amongst domesticated animals. Would it surprise you that cats have played a major role in history with their "jobs?" Take for example the grain storage areas of ancient Egypt. Those grainerys were guarded by cats. It was no wonder that the cat was a treasured animal in those days. Looking at more recent times, the cat was often brought aboard ships to get rid of the Norwegian rats that ended up being taken all over the world by stowing away on those ships.
Many companies all over the world have a company cat or cats to roam their warehouses and keep the mice population in check. England is noted to have more cats "employed" by companies than most western countries.
Give a cat a job – it is truly a great "green" idea, better than rat poisons.