Although it can be deadly, quicksand has no supernatural
  ability to suck a person downward to their death. Quicksand
  is almost always located above a spring, resulting in
  supersaturated sand that lacks the friction to support
  weight. Quicksand is also airless, so any struggle to free
  yourself creates suction that makes it even more difficult
  to escape.

  If you find yourself caught in quicksand, you should lay
  flat on your back with your arms outstretched at right
  angles to your body. You should be able to float on top of
  the sand indefinitely in this position. If you want to go
  one step further and actually get out of the quicksand,
  rolling out slowly to firm ground is your best bet.