A slimy Thankgiving gift from my cat...read on

We were bustling around here getting ready when Brian went downstairs to get something from the basement and said loudly,' What the heck is that?' There at the bottom of the steps laying on a little sunflower floor mat was a dead green garter snake. I am pretty sure my cat Cosmo did him in and left him at the foot of the steps as a 'gift' to us. What I want to know is how he got in? We never had a snake down there before even though a hole is cut in the floor as a drain. We brought in a few big flowers pots a few weeks ago. I sure hope that critter was the one and only snake and I will quote from an Indiana Jones movie and Harrison Ford-'why did it have to be a snake?' Brian picked it up with a paper towel and tossed it down the hill where he could see it. A few hours later it was gone. A nice feast for Thanksgiving for another critter.