啄木鸟在它们的大脑和头骨之间几乎没有“次硬脑膜空间”，所以其大脑不像人类的一样在四周有凹凸不平。

The birds have little "sub-dural space" between their brains and their skulls, so the brain does not have room to bump around as it does in humans.

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其布面凹凸不平，有轻微的按摩作用。

Oil on its rugged surface, a slight massage effect.

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比较两个左和右轮胎，如果一方比另一方，你有凹凸不平的踏穿哪件很可能是造成较大。

Compare both the left and right tyres, and if one side is higher than the other, you have uneven tread wear which is most probably caused by misalignment.

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