Sister Mom / The Laughing

S3, E11: "Sister Mom": When Dexter has to have a "parent-principal" meeting at school, the boy genius is distraught. He's never been in trouble so how can he disappoint his parents now? Luckily he talks Dee Dee into changing her into Mom in his lab so she can go to the meeting in Mom's place. / "The Laughing": When Dexter gets bitten by a set of false teeth belonging to an old clown, he slowly becomes infected with clown's syndrome (something like getting bitten by a werewolf). At night, Dexter transforms into a clown and terrorizes the town. Dee Dee takes mime lessons and is able to save her brother.