Penny inquires as to why Sheldon did not buy Leonard a gift for his birthday. Sheldon explains the irrationality of gift-giving but gives in once he is told it is a social norm.

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Going to Penny's Play

Sheldon does not understand social norms.

Girlfriend's Number

When Raj’s girlfriend abandons him, he feels self-pity.

The Wedding Gift

Howard buys the guys a “Fantastic 4” comic book to celebrate his upcoming marriage.

Spock Being Rational

Penny buys Leonard & Sheldon a Star Trek Transporter.

Stealing from the Charity Bin

Penny feels bad about her past as a bully.

The Endowment Effect of WOW

Sheldon's World of Warcraft account get hacked.

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