使用尽可能少的光线来走动，避免打乱了身体的生理钟。

Using the least amount of light possible to get around helps avoid disturbing the body's circadian clock.

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也就是，公鸡的生理钟让它期待日出，积极地为新的一天觅食。

That is, a rooster's internal clock allows it to anticipate the sunrise and prepare for another exciting day of looking for food.

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又因为公鸡的生理钟有时候设置得早一些，所以，一些公鸡打鸣在日出前。

And because their internal clocks are sometimes set a bit early, some roosters begin crowing well before sunrise.

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