eat like a bird字面意思，吃得像小鸟一样，实际是指“吃得少；饭量小”，像小鸟胃一样。

【例句】
You must eat like a bird if you want to lose weight.
你想减肥的话，就得少吃。

She eats like a bird. A small piece of bread will be enough for her.
她的饭量特别小，吃一小块面包就够了。