Howard and Leonard vie for the affections of Sheldon's visiting twin sister, Missy. Raj participates in a drug test.
- Big Brother Instinct: As the one-upmanship escalates, Sheldon becomes more protective of Missy.
- Early Installment Weirdness: Missy talks about a time when Sheldon built a robot arm to try and keep her from going into his room. As later shown on Young Sheldon, Sheldon and Missy shared a bedroom when they were kids.
- Groin Attack: How Missy corrects Sheldon.
- Insufferable Genius: Missy confirms that Sheldon was one even as a child.
- One Head Taller: Sheldon's usually the tallest, but Missy also towers over all the guys.
- Ordered Apology: What Missy requires. Usually with the aforementioned Groin Attack.
- Special Odd Hand: A mild version. When Raj first takes the drug, his hand starts waving on its own.They mentioned there might be side effects.