Factual error: It's not just the date of La Boheme they have wrong. Pirates of Penzance didn't premiere until 1880 and it was the apprentice who found love with the Major General's daughter and not, as stated, the Pirate King.

Factual error: The morning after Leopold and Stuart travel to the present, the two of them are talking about why Leopold followed Stuart to the bridge. Leopold mentions that he was afraid Stuart might be Jack the Ripper, whose first murder was in 1888, twelve years after Leopold's time.

Continuity: When Charlie and Leopold are walking home after they go to the bar, Leopold says it is after midnight and they should go home. The next scene is back at the restaurant with Kate and J.J. When the camera is on J.J., you can see his watch and it says it's 9:30.

Plot hole: Stuart establishes that there is only one of you and that when you travel through time you can repeat things, but it will be you and not your double that does it. But, at the end, when the Duke is going up the stairs and the uncle says "Where have you been...", the Duke is wearing the same clothes as the first time. Yet we see that he goes directly from the time portal to his house in the ballroom raiment of the later scene. Where did the old clothes come from?

Factual error: In the begining at the bridge ceremony, the band plays Manhattan Beach by John Philip Sousa. However, Manhattan Beach was composed in 1893.

Continuity: In the hospital Stuart tries to grab his neighbor's phone. When he detaches him from his life support and alerts the nurse he holds the receiver in his right hand. The camera changes to a shot from behind, and he picks up the receiver again with his right hand.

Continuity: Hector, the little boy who spends his afternoons at Stuart's place watching TV, is eating from a bag of 'pirate booty' in his lap when Leopold sees him. When he offers Leopold some, the bag is suddenly next to him on the sofa.

Factual error: Leopold recognizes the telephone as the "talking telegraph" he saw at a fair "last year" in the scene where Stuart calls home from the hospital. The first public showing of the telephone was at Philadelphia Centennial Exposition which opened in May of 1876. (He is from April of 1876.) That aside, if he saw a talking telegraph in 1875, it would've been quite a feat because inventor Alexander Bell submitted his patent in 1876.

Continuity: When Leo and Charlie are on the street talking (just before they interrupt Kate's dinner with JJ), Charlie has a cell phone and napkin in his hand, but from one angle it disappears, then reappears in the shot (from a different angle).

Continuity: When Kate is on the top of the roof with Leopold eating dinner, you can see her dress has straps on her shoulders. When the camera shoots back and forth from Kate to Leopold, you can see that the strap has fallen off her shoulder and shows her bra strap. However, when they go back to Kate it is back on her shoulder.

Continuity: When Leopold leaves the apartment with Bart, the leash roles itself up in several loops between shots.

Plot hole: How is it that Kate is completely dry when she is running to Leopold's house at the end of the film? The wormhole is somewhere in the air off the side of the Brooklyn Bridge, and so in theory once you come out of it, kerplunk.

Continuity: During the dinner scene with Kate, Leopold and Charlie, Kate gets up and starts picking up her plate and the ketchup bottle. The shot changes to Leopold starting to stand up, then it switches back to Kate who is picking up her glass of wine instead.

Continuity: When Hector the kid offers Leopold some Pirates Booty - Bart the dog has changed positions on the couch.

Continuity: When Kate tells Leopold that her Sundays are spoilt because the day after is Monday, she cuddles herself against his chest twice in successive shots.

Continuity: In the first heated discussion between Leopold and Stuart a pen suddenly appears behind Stuart's right ear.

Continuity: When Stuart is on the phone with Kate and tries to explain who Leopold is and why he is with him, the clock on his wall moves back by about two minutes when she sits down.

Continuity: Toward the end of the movie when Leopold is making his speech of who he is going to marry, there is a shot of the crowd in the room. In the very back there is a person that runs in and stumbles about. Then there is a close-up shot of Kate coming in and stumbling around the exact same way.

Continuity: In the apartment scene where Kate is wearing a light blue turtleneck sweater and fighting with Leopold, her collar is up in one shot and is folded over neatly in the next.

Other: On the first day at Stuart's apartment Leopold wears some green 19th century trousers he wasn't wearing during his time travel, and which surely weren't part of Stuart's wardrobe.