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When Leonard finally works up the courage to ask Penny out on a date, they each turn to Sheldon for advice.

The Big Bang Theory

The Tangerine Factor

Penny learns that Leonard does not celebrate birthdays, so she plans a surprise party; Sheldon unexpectedly gets to live out one of his biggest fantasies in an electronics store.

The Peanut Reaction

Leonard devises a plan to eliminate his rivals when he, Wolowitz and Koothrappali all fall for Sheldon's twin sister, but his plan backfires when Sheldon decides to choose who his sister dates.

The Pork Chop Indeterminacy

Leonard and the guys buy a time machine prop from a classic movie; Penny tells the guys their obsession with comics and toys is pathetic.

The Nerdvana Annihilation

When Sheldon tries to prove his mental superiority as they train for the Physics Bowl, the guys kick him off the team and bring his nemesis (Sara Gilbert) aboard.

The Bat Jar Conjecture

Sheldon and Leonard look for a way to derail a 15-year-old physics prodigy's research.

The Jerusalem Duality

Leonard and the boys avoid Sheldon when he gets sick, leaving Penny to nurse him back to health.

The Pancake Batter Anomaly

Leonard and Sheldon try to avoid seeing Penny perform after hearing her sing, but the elaborate lie Sheldon tells leads to an unexpected result.

The Loobenfeld Decay

Penny tries to mediate when Sheldon and Leonard disagree on whether to present their joint findings at a physics conference.

The Cooper-Hofstadter Polarization

On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.

The Grasshopper Experiment

Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.

The Dumpling Paradox

Leonard, Sheldon, Wolowitz and Koothrappali attend Penny's Halloween party.

The Middle Earth Paradigm

Physicists and best friends Leonard and Sheldon learn about the social aspects of life through their relationships with the free-spirited beauty who moves in next door.

S1 E16 | The Peanut Reaction