The problem with the latter question is that it's a bit subjective. For instance, one person might say "I've just broken my wrist, but it's not that bad compared to the time I was run over by a train, so I'll rate this as a 4." By contrast, someone else might say "Ow, I've got a paper cut right between my fingers - that really, really hurts! Definitely a 10!" Still, it's a decent starting point.
Of course, if you take this idea far enough, you wind up with Batman:
Batman: "I imagine this is a unique opportunity for you. It must be odd for you to have the chance to catalogue new levels of physical discomfort - as you rarely experience them."
Superman: "What kind of masochist keeps track of the different kinds of pain they've -"
Batman: "Four hundred and ninety-six by my last count."
Superman: "You never cease to amaze me."
(Green Arrow #1, by Kevin Smith)
