Cindy: Oh my god, Brenda, we're gonna die!
Brenda: Well, it would have just been you if you had just shut the fuck up.
When Cindy and Buddy get trapped inside the cold chamber, she starts rubbing him to a point that it becomes masturbation. But when she's sitting on his legs doing the thing, in one side shot you can clearly see she is not holding his privates and her hand is just going up and down, closed but empty.
In the campus garden scene, look behind to the stands. They don't have the most ordinary pictures on them.