"I rolled a 15."
"That just misses. His AC is 16."
"Does that include his shield?"
"But he's running away, he shouldn't get the benefit."
"Facing doesn't affect whether you get your shield bonus." (For those unfamiliar with D&D 3.5, it doesn't generally use facing rules; it's implicitly assumed that you're orienting sensibly at all times, turning to face opponents as appropriate, which helps avoid the sort of "I walk around him and stab him from behind" silliness that can otherwise result from turn-based combat.)
"But he *can't* use his shield effectively while he's running away." (This was a reasonable argument, but I wasn't eager to make a special rule, because there are always some sort of special circumstances, and I wouldn't have dropped the PC's defence if the roles had been reversed.)
"Do you want to use a brain?"
"Right. No shield bonus, you hit him."
Our group has a lot of players whose natural tendency is to try to Wheedle GM at every opportunity (and indeed I'm one of them, when not GMing myself). So I use the brains to resolve this: if you want to Wheedle GM on a questionable point, it costs you a brain. (You can also use them to buy a reroll.) This way, 'line call' arguments can be resolved quickly - either you spend a brain, or you don't. I give brains out as a sort of roleplaying award to players who make me happy (surprising me with clever in-character stuff I hadn't foreseen is a good way to get them), averaging one or two per session. That way they don't have too much impact on play, but they give me a way to show appreciation when players make it fun for me, and help keep the game moving. Has anybody else used something like this?