Rubber-soled shoes will skid on grass, but on most other surfaces they tend to develop too much friction.

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It's been replaced by what's known as "in-fill" turf systems, which cover a football field with 50 million to 70 million 2.5-inch-tall blades of "grass" made from polyethylene, cushioned by a mixture of rubber pellets and silica that acts as the dirt.

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Arlington, Virginia (CNN) -- It may surprise the casual visitor at Arlington National Cemetery to see a rubber duck on a headstone or an old football helmet lying in the manicured grass of a fallen soldier's grave.

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