Or didn't your world have any sciences, Dave Hanson?"  Either the five months under his uncle had toughened him, or the sight of the bulldozer falling had knocked him beyond any strong reaction.
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He had either become more callous under his uncle's guidance or been shocked into indifference by watching the bulldozer fall.
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He'd found himself reacting to things more strongly after spending time with his uncle and seeing the bulldozer fall.