At the carnival, Dick asks Mac if she plans on "popping Cassidy's cherry". Kyle Gallner (Cassidy) was in a movie titled Cherry (2010), in which the main plot point was him being a virgin who had never "popped his cherry".
The trivia item below may give away important plot points.
Cassidy makes a never-explained reference to a "Sally" that seems to uncharacteristically intimidate and terrify Dick. Showrunner Rob Thomas later explained this exchange in an interview with the Newark Star-Ledger: "There's a strange moment that is never answered and there was no way to answer it but meant a lot to me, where Dick looks like he's going to punch Beaver for setting him up with the prostitute, and Beaver warns him, 'I'll get even; remember Sally.' It just hangs there. No one knows who Sally is. We had in our head that Sally was a pet of Dick's that Beaver disappeared after Dick did something to upset him. Beaver has a dark side; he can take care of himself, if you're paying attention. It's tough to get that in there without pointing arrows at the bad guy." Killing and/or torturing animals is one point of the "Macdonald Triad," the three behaviors that in combination are taken by psychiatrists as a strong warning indicator of incipient sociopathy (the other two being fire-starting and bed-wetting after toddler-hood). Since Cassidy helped make homemade "action movies" that included amateur explosions and pyrotechnics, he seems to have been attracted to fire-starting as well, so these references in combination are subtle foreshadowings of Cassidy's criminal insanity.