A moment for Minerva's sarcasm:

Minerva McGonagall: Well, usually when a person shakes their head, they mean 'no.' So unless Miss Edgecombe is using a form of sign language as yet unknown to humans
Minerva McGonagall: I wonder, how you can expect to gain an idea of my usual teaching methods if you continue to interrupt me? You see, I do not generally permit people to talk when I am talking.
Minerva McGonagall: I should have made my meaning plainer. He has achieved high marks in all Defense Against the Dark Arts tests set by a competent teacher.
Minerva McGonagall: Are you quite sure you wouldn't like a cough drop, Dolores?