Upon viewing several commercials centered around stimulation and erectile dysfunction treatment, the duo plan to make a visit to a urology clinic that specializes in sexual performance, after Beavis proclaims that he is "sterile", to which the duo believe meaning not able to score.
Upon arriving at the clinic, the duo firmly hold the belief that the doctor will proceed to offer them women to treat their "sterility." They go through a series of tests; one involving pictures of erotic women, another with a special meter that measures their excitement, and lastly, a physical, to which the two take as the real deal.
As they take off their clothes and lurch towards the attractive nurse, she screams in outrage and leaves the room, demanding that she will not take this harassment lightly. As the urologist walks in, he comes to the conclusion that he "must do this for the future of mankind", and gives them saltpeter.
As Beavis and Butthead walk out the door with the freely offered sexualized women, they continue staring, feeling for some odd reason, they were sexier before. Butthead then administers more saltpeter for the both of them.
Much to public rumor and opinion, saltpeter, aka potassium nitrate, said to be used in the military to reduce sexual arousal, does not bear any conclusive scientific results to be proven as an effective anaphordisiac. The boys are erroneously shown to be having less sexual arousal due to eating it; the doctor likely also under rumor to just administer it for the sake of "knowing" that it does.