In the very first campaign I played in, we spent an awful lot of time pondering a perfectly mundane stone! We actually spent many hours, spread over several gaming nights, studying it...
It started with us being ambushed, hit-and-run-style. The ambushers was up on ledge in a rock wall, bombarding us with crossbow bolts for a couple of rounds, then disappearing as soon as we started to close in on them. When we reached the ledge, the ambushers where gone. "vanished without a trace", was the DMs intention...
However, the paladin rolled a natural 20 when searching the ledga for clues, so the DM figured he had to let him find
something interesting...
"You find an amazingly cool pebble" the DM said. "It's shaped exactly like a tiny apple!"
Of course, we were certain this was important somehow!

It had a disturbing lack of any magical properties what so ever, so we
knew it had to be something
really evil! Maybe it was a key to a portal? The paladin eventually decided it had to some sort of sign from his God; he just couldn't interpret it! He'd recently lost 3 points of INT to a Deck of Many Things, and blaimed the deck for his inability to interpret the "message".
After several weeks of gaming, during which debates over the stone derailed the game over and over, the DM finally broke down and told us the sad truth behind the thing: That he just threw out something utterly silly for the paladin to find, since he'd rolled a natural 20 on that cursed search check.
