Continuity mistake: When Sam tells Al the bartender that he knows another Al who uses the term "caca," Al leans over toward him to say, "Common expression." The camera angle reverses, and Al is abruptly not leaning any more, but standing back from the bar in his earlier position. (00:16:25)
Continuity mistake: In the Japanese bar, when Sam takes a drink from the beer bottle, the label is facing him. When Oswald (who is Sam's reflection in the mirror) takes the same drink, the label has rotated several degrees and is facing outward, away from him. (00:28:15)
Visible crew/equipment: After Sam tells Al the bartender that he wants to talk philosophy, Al tells Sam that he's not just the bartender, he's also the owner, then when Al walks behind the counter the actor's T-mark can be seen on the floor. (00:26:50)
Visible crew/equipment: While Sam and Sue Anne are singing Amazing Grace at the diner, right after the shot of the cook starting to play the harmonica, in the next wideshot the actor's T-mark becomes visible on the floor at the bottom, left side of the screen.
Revealing mistake: The background while Scott is on the raft with Brooke Shields is blatantly a studio wall. The clouds have streaks on them with dark colors and the seam where the ocean meets the wall can be spotted. The film "The Truman Show" used the same technique.
Factual error: Sam leaps into Marilyn Monroe's chauffeur in April, 1960. But the car he's driving her around in is a 1961 Lincoln Continental convertible. The 1960 had prominent tail fins, the redesigned '61 did not, so the difference is noticeable. This is a model Marilyn could not have purchased until, at the earliest, September of 1960. (00:03:00)