Think of that scene:
In the classroom for potions and the like, Neville blanches something pink and undefinable together, Snape anticipates something awful as he sees Nevilles potion and sends him out to destroy it anyhow.
Lupin and Harry just come in, Neville gets up, grabs his "potion" and goes to the door,
Malfoy makes Neville trip and he spills the pink broth over Lupin and Harry, Lupin and Harry become women.
"Professor Snape, I have transformed Harry Potter and Professor Lupin with my potion into women. Can I get an A?"
I think it would be hilarious. XD
But anyway, here are the pictures: