Disclaimer: I don't own Harry Potter (duh) and I also don't own the punchline. Don't know who thought of it first, but I got it from just-shower-thoughts on Tumblr. So there.
It was a regular day, just like any other.
You come to the Ravenclaw Common Room Entrance and you forward to knock.
"What is the opposite of a firefly?" sounds the question. You don't know. So you wait.
A few minutes later, an upperclassman reaches you on top of the stairs. You think he probably knows the answer, but you tell him the question in advance anyway. He says he doesn't know what to say to that. So you sit together.
About an hour later, there's a group about five of you, waiting for someone who understands to come. Some of you have tried to guess an answer, but so far, no luck.
A little group of first years arrive - someone tells them the question and after a beat of silence, one of them starts laughing and pushes through to knock on the door. "What is the opposite of a firefly?" asks the voice.
"The- the opposite of a firefly," he gasps in between fits of laughter, "is a waterfall!" he proclaims finally and the door opens.
A/N: I know. It's bad. What can you do.