[Her expression changes, but only a bit. There's no fear in it, and she's not sure why. Usually she would be terrified of something like this, except for some reason today she's not, today she's ready to go at this from his level.]

For me, you'll wait.

[There's no magic, she just uses leverage - she hasn't got much of it but her gift with numbers isn't for naught, she knows exactly how to apply her body weight, just enough to give her space between them and slip out from under him]

You'll follow the rules to the letter. Catch me in the act, Black. I assume I'll see you at the Ravenclaw-Hufflepuff game next week.

[She winds out and down the hall, and she's back to prim, as if nothing ever happened, before she disappears down the corridor]