Anacondas are some of the deadliest animals out there. They will hunt and attack almost any animal, and they are absolutely ruthless. That is why it is a bad idea to disturb one when you see it in nature.
The man in this video, for some reason, thought it would be a good idea to poke one of these vicious snakes with a stick. He is shown extending the stick towards the snake, whose head is just barely poking out of the water. The snake appears calm and still for a little bit, until it suddenly goes into attack mode and lunges at him. He is clearly shocked and jumps back, but it is obvious that he is laughing a little bit at the very end.
Hopefully, that was nervous or shocked laughter. If he genuinely thought that this was funny, that means that he has really not learned a thing from this situation. He may have found it entertaining, but the reality of it is that he really could have lost his life by poking that snake.
The best thing to do with dangerous wild animals like this is just to leave them aloe if you encounter them out in nature. They can truly be deadly, and the few laughs that you might get from poking a stick at a snake are not worth what that snake can end up doing to you after you do this. Hopefully, if this man sees another anaconda, he just leaves it alone.