First time I ever caught a snake in a leghold trap. Trapping beaver that is flooding farmland. This almost 5' cottonmouth with a head almost 2'' wide was in a #3 trap on a crossover set and his was not happy with his belly pinched.
I saw the end results of a very dead and very large water snake in a 110 that a fellow was using for muskrats in holes in a pond dam. I guess if you are out and about enough you will see strange things. I would say you had a pretty light trigger on that pan.