Context: We’re in this magic mansion that we’ve been to before, and are searching the place for any clues to the whereabouts of someone who used to live there. My Wizard is re-searching the person’s office even though she already searched it the first time.

DM: So, you check around the desk, look through the shelves, all that, and you really don’t find anything you didn’t already see before. *Shrugs like this was a fruitless search*

Me: Yeah, I just kinda go through the desk,

DM: Nothing new

Me, jokingly: Lift up the rug.

DM: There’s a trap door.

Me: …Wait, what?

DM: *nods* A trap door.

Me, still in disbelief: Really? No joke?

DM: Yeah, really.

Me, in character: Holy shit, I was just being funny by checking under here, the fuck is this?

It ended up being a portal to the Elemental Plane of Earth. No big deal.