The Pancake Batter Anomaly
The Big Bang Theory Season 1 Episode 11 (03/31/08)
Penny returns from a visiting family in Nebraska with a cold causing Sheldon to freak out because he's a bit of a germaphone. Sheldon then becomes sick and when he becomes a pain the gang hides from him at a Planet of the Apes marathon, leaving Penny to take care of him. However, when Leonard accidentally breaks his glasses and is forced to return to the apartment, Penny catches him and sticks him with Sheldon. Sheldon then gets sick with no Penny to take care of them.