Remus Lupin: Neville, what frightens you most of all?
Neville Longbottom: Professor Snape.
Remus Lupin: Professor Snape. Yes, frightens all. I believe you live with your grandmother.
Neville Longbottom: I don’t want it to turn into her, either.
Remus Lupin: No… it won’t. I want you to picture her clothes. Only her clothes, very clearly, in your mind.
Neville Longbottom: She carries a red handbag…
Remus Lupin: We don’t need to hear. As long as you see it, we’ll see it. Now, when I open that wardrobe… here’s what I want you to do. Excuse me. (whispers to Neville only): Imagine Professor Snape in your grandmother’s clothes. Can you do that? Yes. Wand at the ready. One, two, three. (opens the wardrobe) Think, Neville, think.
Neville Longbottom: Riddikulus!
Remus Lupin: Wonderful, Neville, wonderful! Incredible!
From Harry Potter and the Prisoner of Azkaban (2004)