Robot physiology: Bender has a beer gut which causes his door to not shut. How?
Future Gender: Fry mistakes the women’s steam room for a co-ed steam room. Leela tries to correct him and observes that Fry’s penis is somehow inferior because it is not genetically engineered; evidently, genetic engineering, contra the professor in season one, does exist, but can only be used very selectively (or is a recent invention specific to season two).
Crustacean physiology: when Zoidberg is heavy with “male jelly”, he feels the need to engage in socially defined masculine displays of physique. His head-fin often unfolds. He gets very hostile to others. Stink glands are important in attracting a mate, though Zoidberg’s are not potent. Love doesn’t exist among Zoidberg’s people: attraction is based on a mixture of social status, personality, and class. Fry teaches Zoidberg to manipulate women.
Claw Plock: a parody of an old Star Trek episode, here, Zoidberg’s people fight to the death over matters of honor and Scrabble. Learning this, Fry makes a homophobic comment: “I didn’t come here to see any activity involving two guys”. It is a recent tradition, only eighteen years old.
The leader of Zoidberg’s people embraces a life of celibacy in order to sustain cultural traditions. At the end of the episode, though, the leader mates; this must be why the tradition is “recent” because leaders keep on mating and dying (the result of mating; makes heteronormativity a convoluted affair but also complicates homosexuality; is masturbation able to occur without death?).
To attract a mate, Zoidberg must attempt an erotic display at the beach; Fry points out whether a bunch of poorly hidden, heavily clothed onlooker are “here to watch the erotic display, too”; thus, we see our second homoerotic reference, and possible homophobic jab: among Zoidberg’s people, there is clearly a same-sex contingent who have no desire to mate with females.
A “shut up” is, apparently, a bird on Zoidberg’s planet.