每日一句（4）

I feel the call of nature.
我得上趟洗手间。
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呵呵，这是外国人委婉的说法，
我们怎么说呢“我去2号”“我要去唱歌”“要嘘嘘。。。”.......

Can u explain why they say as this?
The Call Of Nature Means "大自然的召唤"？

I don't know its derivation.