@FreakyTweakyBleu: That's my best guess, as well. Also, if the horse stays laying on its side for too long, its left lung could collapse due to the weight.
@Hoagie: Doesn't look like makeup removal to me. The blood from his nostril would suggest it's fresh and the different clothes they're wearing would suggest it's a different time/day from the previous page. My guess is he said something dry and snarky enough to piss off one of the other cowboys XD