Continuity mistake: Luke McNamara is handcuffed behind his back at the police station but as he is loaded in to the ambulance he mysteriously is cuffed in front. [The handcuffs inside are normal police issue handcuffs and outside as he's getting into the ambulance they're attached to a belt, normally used for criminals they consider dangerous.]
Continuity mistake: When Lucas is being handcuffed every time it switches shots different police are holding him.
Continuity mistake: During the rowing scene when everyone is racing, the camera goes out to a long shot of all the rowboats and you can see one of the film crew lying down in one of the boats. It can't be the cox - in an eight (which is being used here) coxes can only be seated at the back of the boat. It is considered too dangerous to make an eight a 'front end loader' as he is not as aware of his surroundings.
Factual error: Placing a watch over a fresh brand would hurt a lot and they would be adjusting their watches continuously because of the gross scabbing
Continuity mistake: When Oxford and Cambridge are racing, one of the gates(oarlocks) visibly snaps. Yet in the next scene, the gate has been mysteriously repaired to its former condition.
Deliberate mistake: In the scene with all the coffins and new Skull "recruits", Lucas knocks on the unopened coffin and Caleb pops up. The next shot is a wider shot that shows everyone standing around Caleb's coffin, but the guy in the coffin is not the actor playing Caleb, but a stand-in.
Plot hole: Wouldn't the other secret societies be expecting the Skulls to try to steal their mascot? After all, they claim they have stolen every one but the one they steal in the movie. So that one must know they are next. Yet these Skull wannabes all very noisily and clumsily manage to get the weathervane without any problem. It is hard to believe a secret society would be so easily robbed, especially if they had SOME inclination that the attempt would be made.
Plot hole: A true secret society of that calibre would never allow itself to be known to the point that a perspective pledge would know the deadline for when his last chance would be to become a member.