Penny inquires as to why Sheldon did not buy Leonard a gift for his birthday.

Raj and Howard show Penny the gifts they bought Leonard for his birthday. Penny asks Sheldon why he didn't buy Leonard a gift, and Sheldon explains that he finds gift-giving irrational.

After Penny helps Sheldon with his show, Amy tells him to demonstrate appreciation for her help. Sheldon does so and complains about all of the social norms as he learns about more of them.

Penny buys Leonard & Sheldon a Star Trek Transporter.

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