Raj and Howard try to figure out where Sheldon disappears to every 2:45 PM. Meanwhile, jealousy erupts within Leonard and Penny's relationship.
- Absentee Actor: Amy and Bernadette.
- Brick Joke: In the Cold Open, Sheldon is sketching a containment unit for a small wormhole to serve as a portal to parallel universes. Later, the video he fakes for Howard and Raj has him seemingly creating such a portal.
- ...But He Sounds Handsome: Leonard tries to intimidate Cole by claiming that Penny's boyfriend is large and intimidating, and in a gang.
Cole: She told me he was a scientist.
Leonard: That's the name of his gang. The Scientists. They're crazy!
- Call-Back: As Raj pointed out, 43 is also the element number of Technetium, which was an answer to a Physics Bowl question back in Season 1's "The Bat Jar Conjecture" back when Dr. Gablehauser asked, "What is the lightest element on Earth with no stable isotopes?". Technetium-99m is the most common medical radioisotope used by the world and the United States.
- Camera Spoofing: After finding the camera Howard installed in his secret room, Sheldon prepares a fake video of him making an interdimensional portal and being attacked by an alien.
- Jump Scare: As Howard and Raj freak out over the fake video, Sheldon sneaks up behind them and drops the alien prop in front of them, making them scream extra hard.
- The Peeping Tom: Howard and Raj try to find out what Sheldon writing 43 means in a private room. Sheldon is not pleased that they (attempted to) invade his privacy and punishes them both by inserting false footage of him pretending to be eaten by a squid-like alien from another dimension. And as a bonus, he tosses the squid-alien prop in front of them right as they're watching the footage in horror.
- Shout-Out: Raj thinks 43 is in reference to the Meaning of Life from The Hitchhiker's Guide to the Galaxy. Howard corrects him, saying that it's actually 42.
- Spiritual Successor: To "The Guitarist Amplification", in which Penny also invited another man into her apartment thus making Leonard raise suspicions.
- The Stinger: The audience gets to know what Sheldon wrote 43 for at the very ending. Sheldon is trying to break his record of how many times he can bounce a ball with his knee, and his record was 43. He keeps his ball bouncing private in that room.
- The "I Love You" Stigma: Penny finally says I Love You to Leonard, they're both left overwhelmed by the revelation.
- They Call Me Mister Tibbs: Leonard gives Alex the "Mr. is my father" variant.
Leonard: Call me Leonard, Dr. Hofstadter's my father. And my mother. And my sister. And our cat. Although, I'm pretty sure Dr. Boots Hofstadter's degree was honorary.
- Your Cheating Heart: Subverted, Leonard suspects that Penny is cheating on him since she invites her college friend Cole into her apartment for a history project.