Task: Question Generation
Input (English):  "Zerophilia" is a fictional condition that affects an unknown number of people with an extra "Z" chromosome. Following their first full sexual experience, zerophiliacs begin to change sex after experiencing an orgasm. Luke (Taylor Handley), a young man somewhat insecure about his masculinity, begins to exhibit zerophilia following an encounter with a woman (Kelly Le Brock). He meets Michelle (Rebecca Mozo) and experiences partial transformations when they go out together.
He confides with his best friend Keenan (Dustin Seavey) about his partial transformations, who in turn contacts Dr. Sydney Catchadourian (Gina Bellman). Dr. Catchadourian persuades Luke to go through a full transformation. Luke does this by masturbating, becoming female, and subsequently calling herself "Luca". Luca has difficulty achieving an orgasm to change back, even with coaching from Keenan's girlfriend Janine (Alison Folland). However, a visit by Michelle's attractive brother, Max (Kyle Schmid), who flirts with "Luke's cousin", enables her to get sufficiently aroused to complete the transformation back to Luke.
Luke is threatened by his sex transformation, his arousal by an attractive male, and the questions of sexual identity it raises; he seeks help from Sydney. She tells him that a zerophiliac can become "a-morphic" and stop changing sex only by having sex with another zerophiliac... such as herself. He reluctantly agrees to do it, but discovers afterward that she was not telling him the full truth: an a-morphic zerophiliac can still change by having sex with another zerophiliac, and Dr. Catchadourian was using Luke to change herself one last time (into a man), leaving Luca as a woman in the process.
Comic tensions arise from Luke's efforts to keep Michelle at a distance, Max's defensiveness about his sister, Luca's half-hearted resistance to Max's affections, and Luke's confused aggression toward Max. When Michelle discovers that Luke had sex with Dr. Catchadourian, she feels betrayed. Hoping to find Michelle, Luca seeks out Max to profess deep affection for Michelle and remorse for betraying her. Max is touched by the apology, and reveals that he is actually Michelle, also a zerophiliac. They make love repeatedly, changing sex mostly in sync with each other, but occasionally finding themselves the same sex. It ends with the happy couple apparently resolved to their 'condition' and past any questions of their sexual identity.
Output (English): What physiological event triggers transformations in zerophiliacs?