So, to set the scene: our heroes have returned to a mummy-infested dungeon beneath a merman prison, intent on slaying the vampire that lies within. After a particularly tense battle with some peskily-regenerating mummies-- resulting in several infections of mummy rot-- two of the PCs, sherriff Feer and her deputy Jarmangle, decide to arm themselves with a couple of torches that they can throw at the flammable mummies.
Soon thereafter, they come to a doorway. Said doorway is blocked by a mass of foilage with little, closed-up flowers. Their usual modus operandi when faced with a suspicious-looking plant is to stand back and set it on fire. This I'm kinda counting on: the flowers, which of course unleash a poison gas when they open, are heat-sensitive, and the door through which they entered this room will not stay open. Bwahahaha, et cetera.
But my players don't set it on fire; instead, they begin investigating the plant. Feer and Jarmangle notice when they come near it that the petals start to open slightly (though not enough to unleash the poison); the others, however, don't set it off.
"Huh," said Jarmangle and Feer at about the same time. "Why does it just do it around us specifically? What do we have in common?"
The answer, of course, are the flaming torches, but they don't think of that. Instead, they each begin looking through their loot. We're both wearing hide armour, maybe it's the hide? Jarmangle takes his armour off. Nope, he still sets it off. They have swords? Jarmangle puts down his sword. Nope, still setting it off.
Repeatedly, they flip through the 3x5 cards on which are written their various possessions. Briefly, the possibility that they are both law enforcement is considered. They go through the cards again; they pass them around the table. "What is it that we have in common?"
And by this point I'm laughing hysterically.
"Maybe it's something you acquired recently," I said, trying to be helpful.
They mentally retrace their steps, but they forget about the torches.
Jarmangle finally says, "Okay, I'm taking off everything. Putting everything down. Completely nekkid."
"Everything?" I said. "Including the torch?"
What was so amusing to me about this was the image of these two inteprid adventurers, each holding identical torches, scratching their heads: But what do we have in common?
It's the sort of experience that could only happen at the gaming table; you'll never see the scene replayed in a fantasy novel. For me, that makes it special-- one of my favourite moments of my DMing career.