It was filled with a waxlike substance, the middle of which had a round indentation, in the shape of a small ball.

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In particular one part of it - calcium silicate hydrate - refused all attempts to be analysed under an electron microscope or by nano-indentation.

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This rocker sits flush with the side of the device, the indentation in the middle serving as the only thing that sets it apart from the left extent.

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But "every one of those stops was memorable, " Closson says, explaining why, despite a black eye and a permanent indentation in his head, he signed up for Nemitz's trip through Tuscany in 1998.

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