Snake! back yard.

Memike, I hate to sound all preachy and PETA-like, especially since you did not enjoy doing it, but many snakes mate for life. If you kill one you are killing scores of them because you just killed a mating pair and all their potential descendents. Nature can be cruel and may cost you some squirrels but you really should not interfere. Too many squirrels sucks too. You have to take action if you find a dangerous species establishing itself on your property but you should leave the harmless ones alone. Just my two cents worth.