Professor Duncan suggests Garrett go kill John Lennon again. This is a reference to Mark David Chapman, who bears a slight resemblance to Garrett.
In the first scene at the classroom of Spanish 101 there is a map of Mexico hung upside down over the right hand side.
Professor Duncan's (John Oliver) incompetence as a psychologist is even more apparent with his explanation of his experiment. By talking about the Id and the Ego, etc, he reveals that his "Duncan Principle" is founded on Freudian theory and so not original or adding anything new to research. He would never be able to get it published, or even approved in the first place by the Institutional Review Board to do this kind of experiment on humans.