In the shot in the bathroom, Tanya has a small diamond necklace but in the next shot in the bedroom the diamond appears larger.

In the very beginning of the movie, Ben is seen riding his bike over the bridge in an aerial shot. Near the top of the screen, if you look carefully at the end of the bridge you can see a police barricade at the end of the bridge. It is there because the bridge is closed for filming.

As Juno is walking into the abortion clinic, an exterior shot shows that there is only one entrance door. The shot of her entering from inside the clinic shows a double-door entrance.

The entire movie hinges on something that is an impossibility. One's twin cannot remove a biometric lock from a machine. This might be possible if it only compared DNA, as identical twins have the same DNA. This, however, is where the similarities end, as a hand scan would have been invalid, because of different fingerprints. The facial/retinal scan should have been invalid because the retinas would have been different, as well as their faces, as a result of different environments (i.e., scars, hair, facial hair, etc.). Finally, and the biggest hole, the voice print scanner. Maybe they would have been similar enough for comparison; however, I simply cannot believe they would have been identical.

When Jack Black's character is tied to the tree, he changes from having trousers to having just Y-fronts on several times. Usually happens between shots of the group and shots of just him.

In the scenes in which Brennan and Dale are fighting with the young children in the park, it is clear that in quite a few shots the children have been replaced with doubles.

In the scene where the fat man walks in on Peter naked in bed, the sheet protecting Peters modesty is covering him in one frame, and the next moment it has vanished completely.

In every car scene in the movie that you look at Kate's glasses, you can see the green screen used reflecting off her glasses.

When the Silent Monk and the Jade Warlord are fighting, the warlord wounds the monk in the right shoulder, next shot the bleeding wound is gone, but it reappears once again in the next shot after that.

When Johnie Quid is telling his mate about the warnings on a packet of cigarettes, the warning reads, "Smoking kills." But, as the close-up blurs out, the warning suddenly reads, "Somoking seriously harms you and others around you."