For my money, the first thing should be whether it is running from you. If it is running from you, leave it be. I grew up in Florida where you could stumble across the occasional cottonmouth. We left them alone and they left us alone. Most of nature is like that, and I like it that way.
No need to ask for trouble.
Our snakes aren't especially in a hurry unless they're crossing the road. Whodathunk that snakes could learn to cross the street. Local lore has stories of very aggressive cottonmouths that actually chase people, but we haven't seen that. They're not interested in having a close relationship with us, but aren't particularly impressed with us, either. We have copperheads, too, but have only seen shed skins. (The dogs bring them to us as gifts.)