Years ago I knew someone who owned an apartment with an attached store and craftsman factory (handmade stuff, so not really a "factory") in Greenwich Village. There was a woman called the Cat Lady who hung around and sold cats as mousers. This guy had two of them he kept in the basement. He NEVER fed them - they lived on mice. And they were the fattest cats I have ever seen in my life. I just got grossed out looking at them knowing they were filled with mice
