Anaconda is a biggest snake in the world.

Member of the boa family, South America’s green anaconda is, pound for pound, the largest snake in the world. Its cousin, the reticulated python, can reach slightly greater lengths, but the enormous girth of the anaconda makes it almost twice as heavy.
Anacondas in the wild spend most of their time hanging out in rivers hunting for their food. They are solitary creatures that are somewhat shy and not many of them are easily seen. They are very well camouflaged in the swamps and bogs in which they thrive. There are some historical reports of early European explorers of the South American jungles seeing giant anacondas up to 100 feet long and some of the native peoples of the South American jungle have reported seeing anacondas up to 50 feet long.
Anacondas live in swamps, marshes, and slow-moving streams, mainly in the tropical rain forests of the Amazon and Orinoco basins. They are cumbersome on land, but stealthy and sleek in the water. Their eyes and nasal openings are on top of their heads, allowing them to lay in wait for prey while remaining nearly completely submerged.
Just about every species of snake on earth has teeth, but the anacondas' teeth are not used for chewing. Snakes' teeth are used for holding onto their prey, preventing them from escaping. Some snakes have venom in two specially designed, extra long teeth (called fangs) which they use to kill their prey. Anacondas have teeth, but they are not a venomous snake. They rely on their enormous size and power to subdue their victims. It is possible to be bitten by an anaconda, but the bite itself would not be fatal.