Mr. Green: So, how did you know Colonel Mustard works in Washington? Is he one of your clients?
Colonel Mustard: Certainly not!
Mr. Green: I was asking Miss Scarlet.
Colonel Mustard: Well, you tell him it's not true.
Miss Scarlet: It's not true.
Professor Plum: Is that true?
Miss Scarlet: No, it's not true.
Mr. Green: Ah ha! So it is true!
Wadsworth: A double negative!
Colonel Mustard: A double negative? You mean you have photographs?
Wadsworth: That sounds like a confession to me. In fact the double negative has led to proof positive. I'm afraid you gave yourself away.
Colonel Mustard: Are you trying to make me look stupid in front of the other guests?
Wadsworth: You don't need any help from me, sir.
Colonel Mustard: That's right!
When Miss Scarlet reveals her profession Mr. Green puts two and two together.