I have a Tokyo Marui MP5K-PDW just for shooting at the birds, squirrels, and cats in the yard. Since it won't really kill a bird, I can even run the Texas state bird off (Mockingbird) with it.
I have scared the holy bejesus out of a few cats with the thing. It is truly fun to hit them suddenly with full auto.
I also got it for practice around the house. I have the real thing and want to be able to produce a replica if someone starts asking about why they saw me with a machine gun around the house.
About six months ago, I had a neighbor and his small dog stuck on my front porch because another dog had cornered them there, trying to get at the small one. I snuck out the house and around the side. That dog couldn't get away fast enough when the pellets started hitting his hind quarters.
The beauty of airsoft is that it's a kid's toy (sorta) and no one can really charge you with anything for shooting the neighborhood pests with it. Well not in my neighborhood anyway.