Strange things happen after hours and hours on the trail. Take for instance my experience on this year's Arrowhead 135. At around 4am the day after the race started (almost 24 hours into it) I became convinced that a gaseous emission some several hours earlier might have contained some particulate matter (or large chunky matter). I finally couldn't take it anymore as the idea dragged at my addled sleep deprived mind and I stopped to have a good wipe. Sadly I hadn't brought any bathroom papers with me and grabbed the cheapest most disposable item of clothing I had with me, my face mask (I had several spares after all, even one exactly like the one I "used"). As it turns out, it was of course in my head and I basically wasted a good face mask. It's a funny story that comes to mind when gross stories and trail stupid come up.
It isn't something you remember at six am when you are desperately trying to find your face mask so you can get out of the house and on your way to work. After all, I know I bought two of those things.