"Do not assume all snakes are poisonous," I told myself.* "That one you saw the other day was probably a brown water snake. Not all snakes are poisonous. Surely there are plenty of other other snakes that look exactly like cottonmouths." I went home and looked on line. There are indeed some look-alikes. So, banded water snake, or mature cottonmouth, Ursula isn't going to go prodding this legless gent to find out for sure.
When it saw me checkin' it out with the binoculars (I was maybe ten feet away, but I wasn't getting any closer) it slithered into the bushes. This doesn't mean anything--despite their reputation as some kind of scaly psychotic, cottonmouths, like the vast majority of snakes in North America, would much rather flee than tangle with you. (I recall a show once where several scientists set out to see just how aggressive cottonmouths were. At one point, they were standing around poking the thing with sticks, trying desperately to provoke an attack, and the snake was just "Let me go, let me go, I have no quarrel with any of you, let me go, let me go." They eventually concluded that as long as you don't step on them, and don't try to play with them, you'll probably be fine. This is good advice with any animals, and most artists.)
*Unless you're thinking of handling them, in which case all snakes are not only poisonous, but explosive.