We've had fights here, well, tiffs usually. There's the typical yelping - and if one is bitten, you can't see the bruise, no. The fur covers it. Doesn't mean it doesn't hurt. If no actual contact/bites occurred, they usually don't hurt, no.
But have you ever seen a puppy get injured mildly (tripped or fell a little ways, like from a step) they'll scream like there's no tomorrow.
That's more of a "I want my MAMA!" shriek than anything, borne of being startled.