Okay so I think I've seen this challenge somewhere before ... maybe I'm just remembering WLIIA :D
Okay so what will happen is: when you enter, I will give you three lines (for example, "Not that one" "Only when she says so" and "No, it's over there") and they are to be the ONLY three lines used by a character in your story. The character can be any, the plot, genre, pairing is all up to you... you can write a Riddle/McGonagall with Dumbledore as the Limited Lines Character if you want. It's up to you, but whichever character you choose (be it a prominent or minor one) is ONLY ALLOWED TO SPEAK THE LINES ALLOCATED. They can gesture, think, etc, anything you want.
I will give a bit of leeway: one of the lines will have some options on a word. See below for examples :)