Leonard is shocked when Penny claims their first kiss was at his birthday party. Leonard correctly recalls it happening at a Halloween party (Season 1, Episode 6, "The Middle Earth Paradigm") where Penny was drunk and upset over her ex, Kurt. Penny later admits she remembers but prefers the birthday memory because it actually meant something to her.

The Imitation Perturbation | The Big Bang Theory Wiki | Fandom

Season 12, Episode 6, is the final Halloween-themed episode of The Big Bang Theory and is widely remembered for its sharp character parodies. Key Plotlines

Howard arrives at work dressed as Sheldon, mimicking his "spot" and bathroom schedule. Hurt by the ridicule, Sheldon and Amy retaliate at Leonard and Penny’s party by dressing as Howard and Bernadette. Amy’s "spot-on" high-pitched impression of Bernadette is a highlight, though it causes genuine friction between the couples.

The storyline was loosely based on a real event where a writer for The Big Bang Theory was parodied by a colleague while working on Malcolm in the Middle .

Leonard's Inspector Gadget propeller was originally so long it hit people on set, requiring the wardrobe team to cut it down several times for balance.

Anu's U.S. Constitution costume featured the Bill of Rights on the back, which the costume designer researched at the National Archives website to ensure accuracy.