There were two things that Douglas wasn't in any mood for : one, crossing paths with Nigel, and two, getting up at night. So in short, getting up at night and bumping into Nigel bolting back to camp was a bit of a worst case scenario. Bumping into him so hard they fall on top of one another in the foliage drove him over the edge.

“Yo watch where you run white tail, what's wrong with you??” he screams. “Still scared of that dumb story or of being caught looking dumb and naked??”
“S...sorry.” Surprise at the yelling, the deer froze in place keeping Douglas pinned down on his back.
« HEYY !! Get off me !! GET OFF MEE !! »
« Shh, quiet... » Nigel whispered, trying in vain to calm him down. “You'll wake the others...”
« LEMME GO !!! »
Nigel panicked, his overly active self-preservation instinct demanding an immediate solution before more people would be alerted and come investigate; seeing how both his arms were in use, he went straight to shutting Doug's mouth using his own. This was quick to work.

« YUCK! Now will you keep quiet? I don't wanna have to do that again. »
“Huh... heh, you could've ASKED, ya know...”