The Best Episodes Written By Stephen Engel

Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.

Sheldon and the gang are confused when a young grad student is attracted to him.

With his friends knowing how sour he acts when sick—and avoiding him as a result—Sheldon is nursed by Penny, who hasn't a clue what she's in for.

When they're invited to present at a physics conference, Sheldon's reluctance to share the credit leads to a tiff between him and Leonard, and Penny's intervention only exacerbates the situation.

Sheldon finds himself booted from the gang's Physics Bowl team and replaced with Leslie, so he forms his own team, hoping to prove he's superior.

Raj gets an inflated ego and makes a play for Penny after being referenced in a magazine article.

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is on board the train they are taking to San Francisco.

When delivery of another collectible leads to Penny's lashing out at Leonard, he decides it's time to give up his habit, much to his friends' protestation.

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.

With Sheldon rattled over meeting Dennis, a 15-year-old physicist who's smarter than he, Leonard helps him look for a way to debunk Dennis's research.