An interrogation technique that consists of asking innane irrelevent questions, and then suddenly, ham-handedly asking directly if the person is guilty of whatever you are investigating and hoping they will slip up and just confess. The term refers to the News Radio episode "Jail (part 1 of 3)" where Matthew is interviewing Jimmy James and trying to determine if he is D.B. Cooper.
Of course Monica denied she's screwing your brother. You've got to be subtle when you lay the trap, you can't just Doobie Keebler her with the question.