A friend of mine asked me to bathe her dog. She was feeling ill and the dog really stank. She gave me a little bit of money for helping her out. About a week later, another friend asked if I could help bathe a stray kitty she found. Same thing, I got a little bit of money.
I put an ad in the local paper that I would assist with pet bathing. Since then, I get calls for dogs, cats and even a ferret. This is a good side biz because there is no startup cost. Also, you can just let a few people know and work as little or as much as you want to.