I came across a blog called Acid Test (found via Blog on the Run) that posted what is supposedly an excerpt from a Peace Corps training manual.  It details how to respond to being attacked by an anaconda.  To wit:

“Related to the boa constrictor, the anaconda is the largest snake
species in the world. It grows to thirty-five feet in length and weighs
300 to 400 pounds.

• 1. If you are attacked by an anaconda, do not run. The snake is faster than you are.
• 2. Lie flat on the ground. Put your arms tight against your sides, your legs tight against one another.
• 3. Tuck your chin in.
• 4. The snake will begin to nudge and climb over your body.
• 5. Do not panic.
• 6. After the snake has examined you, it will begin to swallow you
  from the feet end – always from the feet end. Permit the snake to
  swallow your feet and ankles. Do not panic!
• 7. The snake will now begin to suck your legs into its body. You must lie perfectly still. This will take a long time.
• 8. When the snake has reached your knees slowly and with as little
  movement as possible, reach down, take your knife and very gently slide
  it into the side of the snake’s mouth between the edge of its mouth and
  your leg, then suddenly rip upwards, severing the snake’s head.
• 9. Be sure you have your knife.
• 10. Be sure your knife is sharp.”

Have fun sleeping tonight.