Duck/Aren't You Chupacabra to See Me? - S4-E9
Continuity mistake: Mandy is in the library working on her report. When she's working on the second page, the writing is scribble, and on top of a stack of paper. A second later, the page says "CORN by Mandy", and the stack of paper is gone.
Episode XXIX - Couple on a Train - S3-E3
Continuity mistake: On the train, Josephine walks past Jack when he's given his cup of tea. In this shot of Josephine, her facial beauty mark is on her left cheek, but in previous and following shots her beauty mark is on her right cheek. (00:07:35)