When you're really tired sleep is what you want to do like when you're really hungry you want to eat.

你累了，就会想睡觉,正如你饿了想吃东西一样。

耶鲁公开课 - 心理学导论课程节选

It means that we want to eat when there's food around, and it doesn't matter so much whether we're really hungry.

这就意味着只要周围有食物我们就想吃,不管我们是不是真的饿了

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选