As Kid flies over the pond on the bike, he is suddenly wearing a helmet (to hide the stunt double). In the following shots, he's wearing his cap again.
During the sequence with the car in the kitchen, a crack in the windshield appears and disappears.
Ben removes one wheel from Kid's truck and tethers it to the ground with a pole and chain. When the buggy is destroyed a short time later Kid's truck has the wheel back on and is untethered.
During the last fight scene, the amount of balloons on the floor goes from ankle high to chest high.
The weapon the assassin Paganini has is described by the doctor as a Remington 77, while in fact it's a Brno Fox 2 in caliber .222 Remington.
Stunt drivers visible in the burning car.
Electrical sparks under the amusement park's rocket cart challenge reveals it's actually under power.
Tire tracks from the camera car during the chase scene in the forest.
At least in the German version, the conductor at the opera in the end says: "I'm leaving Italy" - it is obvious that the movie is not set in Italy but in Spain instead.