People writing textbooks clearly know that they don't have your full attention. Which is why some took the liberty of sneaking in a couple of Easter Egg jokes to reward the few, the proud, and the studious who went out of their way to read photo captions and footnotes.

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via aereeve

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via Brock__Lee

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via Distroyer32

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via R4ndomosity

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via to__blave

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via tatanka_truck

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via Karmanacht

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via ismo420

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via scottg96

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via olster1

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via magicwings

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via Codexlibero