Wiktionary
vb. (context euphemistic English) To satisfy the bodily urge to urinate or defecate.
Usage examples of "answer the call of nature".
At the same time Adriano, not by reason of the noise, which he heeded not, but perchance to answer the call of nature, also got up, and questing about for a convenient place, came upon the cradle beside the good woman's bed.
As Borric watched, the man stood, and moved into the flow of traffic, leaving behind fresh proof he hadn't been squatting to say devotions to some god, but rather to answer the call of nature.
I fear not the cold: 'tis seldom indeed, when I leave my bed a nights, to answer the call of nature, as one must at times, that I do more than throw a pelisse over my doublet.
It never left her side for more than two minutes to answer the call of nature.
So if you want to be able to see where youre walking after you answer the call of nature, you better go now.