Normally, biologists explain this as being either nepotism or you-scratch-my-back-and-I'll-scratch-yours.

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As I tuck my pen into the place between the top two buttons on my shirt, I scratch my chin and the back of my head although neither itches.

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"I was bending over to scratch her back with my hand, " she wrote under the photo.

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"The more remote the location, the more I scratch my head and say, 'They are never coming back, '" Mr. Forster says.

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