This video from the USA says about itself:
18 November 2016
The Water Moccasin or Cottonmouth snake is the venomous snake a bird watcher in Florida is most likely to encounter. This video shows that the typical behavior of this beautiful snake is to freeze and then move away slowly and only display a threat of the wide open “cottonmouth” if you continue to invade its space. It goes without saying you should not mess with them!
After a few minutes of admiring and slightly annoying this majestic snake I let it move on into the roadside canal. The real danger with these snakes is that since they are heavy and not fast, they freeze in deep cover where they are near impossible to spot and if you’re walking in heavy grass and brush you might accidentally step on them leading to a leg bite and a life-threatening situation. I recommend staying on trails if at all possible and being very careful around the edges of wetlands.
(Agkistrodon piscivorus conanti)
Comments: VENOMOUS: Cottonmouth bites can be quite dangerous. The victim should seek immediate medical care from a physician or hospital experienced in treating snakebite.