Quicksand is a mass of sand and mud that contains a large amount of water. A thin film separates individual grains of sand so the mixture has the characteristics of a liquid. Quicksand is found at the mouths of large rivers or other areas that have a constant source of water. Heavy objects, including humans, can sink when encountering quicksand and the mixture collapses. However, since the density of the sand/water mix is slightly greater than the density of the human body, most humans can actually float on quicksand.