A very large snake. Posesses fangs, no poison i think. Will try to swallow prey whole, not constrict. There is a simple plan of action for if you are attacked by an anaconda.
Lie down on your back, with your arms by your sides and your legs together. The snake will crawl over you, checking you out. Do not panic. The snake will then try to swallow you. It will dislocate its jaw, and start to swallow you feet first - always feet first. Allow it to take you in its mouth up to your knees, this will take some time. When the snake reaches your knees, slowly pull out a long, sharp knife and isnert it between your knees and the anaconda's top jaw. Slide the knife away from you with force, hence removing the anaconda's head. The anaconda will then die, and you will be able to safely remove your shins and feet, and leave unscathed. You will not, however, be able to carry away the dead anaconda. It is simply too big.
So, now you know how, you will be able to protect yourself from anaconda attacks in any place you find them.