When Harriet offers Charlie a "health shake" with strawberries, the glass initially has no (or very little) ice, only foam. Subsequently, the shake suddenly contains a lot of ice.
When May opens the Weekly World News in close-up, she turns only the first page. It then cuts to a longer shot and about three more pages are turned.
When e first see the honeymoon hotel (in reality Dunsmuir House) there is a tower that is not there in on the real hotel. Regardless of that, in the second shot of the hotel, the tower is missing. Also, there are no mountains/cliffs in the background.
Charlie is helping out in the butcher shop and he is wearing an apron cutting meats, but the next scene he isn't wearing an apron and then the next scene he is wearing one.
The first customer in the butcher shop is shown being handed her purchased material, then leaving the shop. In the montage that follows this scene, she is again shown when Charlie says "Mom, help! It was an accident in shop."
In the Alcatraz scene cells are shown with swing doors, some of which are open. All of the cells in Alcatraz have sliding doors.
The tartan pattern worn by all the Mackenzie men at the wedding isn't that of Clan Mackenzie.
Alcatraz Island Ranger Vicky states that many of the Park Rangers are former guards of Alcatraz, including himself. The prison closed on 21 March 1963, 30 years prior to this movie. This would have made Vicky a teenager at best when the prison closed, and too young to be employed as a guard. However, Ranger Vicky is most likely just telling a tall tale.
Anthony LaPaglia (Tony) corpses (breaking character by laughing) several times when he is watching TV with Charlie's Scottish father Stuart, particularly during Stuart's rant about Colonel Sanders.
When the honeymoon inn emcee is announcing the newlyweds, the first word he is heard saying is "Folks," but his lips don't start moving until the second word, "to." In fact, he ends the same sentence in the repeated words "folks," so this was probably a mistakenly repeated word when the monologue was re-recorded for the film's audio.
When Charlie and Harriet are in bed, her mouth is not in sync with her voice.
When Charlie is offered the "health shake" and retreats into the closet, a man wearing a red ball cap can be seen crouching in the lower left hand corner of the screen.
There is not, nor has there ever been, an outdoor cafe in the location (relative to the Golden Gate Bridge in the background) where Charlie and Harriet eat hot dogs during their initial romance montage.
When Charlie meets Ralph and after Charlie loses his towel, Charlie is leaving to go upstairs and says, "nice to meet you, Linda".