"I can't see through the cloud of blood!"
That is a quote by my friend Max (yes, the previously mentioned Max). He and I and another friend of ours were playing F.E.A.R. Or maybe it was F.E.A.R. 2? Either way, there was a point during our run through of the video game at which enemies were flooding our small office room stronghold so fast, and Max (who had the controls) was pumping shotgun shells into the crowd so intensely, that the first-person shooter screen was just a cloud of red particles.
"Get out of there! Get out of there!" I yelled. "There's more coming in!"
"I can't see through the cloud of blood!" Max yelled back.
It turns out that Max did very well. There was only a single, badly injured enemy left once the gore-cloud settled. But there was panic there for he and the rest of us in front of the TV, because for a moment, our victory seemed to be going up in bloody smoke.
That doesn't happen much in pen and paper games. Without some kind of Deus Ex Machina on the side of the PCs, or the enemies, once one side gets the upper hand, it's pretty much all over.
Occasionally, a random fumble will net the fighter a dropped weapon, or a double critical hit will take out the bard (eh...), but other than that, there is very little that truly happens randomly in combat. If someone isn't swinging a sword or slinging a spell, the rest of the world is just constant and, well...dull.
What if the fighter's weapon got stuck in the enemy's body, or armor, after they attacked? They don't have to let go, but if the $h!t is still hitting the fan, he may want to begin considering a secondary weapon. (Hey! Now your fighter has a reason for carrying that secondary weapon!)
What if the fireball set off by the wizard incinerated a bunch of grass and sent up a cloud of dirt and dust? Uh oh, now there is concealment to deal with, and that stuff blows around with the wind before it settles.
Here we go. The slimy blood and bile of that giant you just gutted is making it extremely hard to hold onto your sword. It may be time to go fisticuffs to save yourself the "keep your grip" checks.
I guess the point is to escalate the challenge when the players are doing really well. Let them keep rising to the new occasion, rather than just having them stomp all over an encounter or challenge that they rolled way above average for.