For the first in my series of extensive, dry and beardedly patronising lectures on the positively minute number of things I've learnt while writing and thinking about bonking, I'm going to discuss a particularly thorny and complex issue.
Namely, never mention that your characters need a poo.
Just don't do it. Don't do it ever!
I know the urge is there. I know you might think to yourself: but everyone poos! It's realistic, to have my heroine say "God, I really need a poo".
But resist. You must resist.
If the urge overwhelms you, try phrasing it a little bit more like: "God, I need a crap" or "I'm just gonna go take a crap". Somehow, that just sounds more palatable. More grown up, maybe, and less about things you do in the potty? I don't know.
Just please. Say no to poo.
And thus endeth my first in this series of deadly serious lectures, that I carry out while wearing and stroking a beard.