Desk Cheat

Method of cheating at school that consists of a student asking about one of the multiple answer questions to the teacher and another student knocking on the desk repeatedly. The number of knocks is equal to one of the answers, so if the other student knocks on the desk 2 times, it's option B.

Student 1: Teacher, what do I have to do in question 3?
Student 2: *knocks on desk 3 times*
Student 1: (Thinking) So it's option C! Thanks for the desk cheat...