Snakes can give you a lot of trouble in Red Dead Redemption 2. But encountering a giant snake would be a completely nightmarish scenario, one your horse might soon like to forget.
Fortunately, you will find out that this Easter egg is all show since the snake's already dead. Based on what we know about Rockstar's quirky sense of humor, it's safe to say this Easter egg was put in for scares, and not much else. But in any case, a giant snake is a sight to behold.
You can find it by traveling to Lemoyne region in the forest south of Pleasance. It will be hanging from a tree at the edge of the forest.