Very quickly, the sand sinks to the bottom and the water floats to the top. This is where the salt comes in. When there’s enough salt present, as soon as the clay particles liquefy, electrical charges make them begin to stick together to form bigger particles and these also settle with the sand. Quicksand is a mixture which looks like solid, but behaves more like a liquid.

　　Despite its murderous reputation, quicksand does not such people under and swallow them, although it can hold a person in firm grip. The human body is more buoyant(有浮力) in quicksand than in water, and sooner or later anyone trapped in it will float.

　　Unlike most liquids, quicksand’s viscosity, or “runniness” can suddenly change if it comes under pressure, for example under a human foot. The surface gives way and the victim quickly sinks in up to the knees, surrounded by an area of dirty things that turns semi-solid around its victim. Escaping from the quicksand’s grip(紧握) requires a large amount of force. Without something solid to pull at, people often find they are stuck fast. Pulling at one leg simply makes the other one sink further.

　　So how do you escape from quicksand’s control? Stay still and call for help. Staying still stops you sinking any further, until--with luck--help arrives on the scene. If no one appears and you need to draw yourself out, gently lie down on your back until your body is floating on the sand. Next, roll over onto your stomach and pull yourself forwards with your hands, so that you gradually “swim” towards firmer ground. It is a slow and dirty business, but it works.

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