Revealing mistake: When Benny the Cab jumps onto a bridge with Roger and Eddie, a red Ford De Luxe skids to avoid a collision. Notice how tire tracks from a previous take are visible on the pavement. (00:59:35)
Revealing mistake: After Bongo the Gorilla Bouncer tosses Eddie into a pile of garbage cans in the back alley, Eddie lifts himself up and here we can see that he's wearing knee pads beneath his pants. (00:21:25)
Revealing mistake: After Roger reads Marvin Acme's will out loud, all of the toons start jumping for joy. Meanwhile the music machine is still activated in the background, and its colorful flashing lights are being reflected on the ground near Betty Boop and Tweety at the front of the crowd. With all of the toons grouped together like they are, the machine's colorful lights should have been obscured, not reflected. (01:35:30)
Factual error: When Judge Doom is at the window of R.K. Maroon's office firing his gun at Eddie, a photo of R.K. beside the armchair takes a direct hit, but only the glass frame gets shattered. Unless it was bulletproof, the picture should have been pierced right through. (01:07:10)
Revealing mistake: During the Toon Patrol chase, before the cab enters the alleyway there's a wide shot of the cab making a fast turn. Valiant has his head down, with his hat covering his face and his body totally motionless, opposite to what he looks like in the close-ups where he is grabbing the steering wheel, his head up and controlling the car, thus revealing that the actor was replaced by a dummy in some of the shots. (00:58:40)
Continuity mistake: At the end of the movie, when the spray-machine breaks the brick wall with the word 'Keep Clear' painted on it, the first 'E' and the 'A' get destroyed, but appear rebuilt a second later.
Continuity mistake: When Doom writes on the bar's blackboard "Rabbit Dip" the look of the text keeps changing all the time: sometimes it's neat, others it's fuzzy, and others some letters are missing. (00:52:10 - 00:53:10)
Continuity mistake: When Eddie hitches a ride on the back of the Streetcar, only its rear power-arm is attached to the overhead cable. Later when Eddie jumps off and says "Thanks for the cigarettes", it has both of its power-arms raised. (00:10:10)
Continuity mistake: In the scene after Valiant gets rejected by the trolley operator, notice as the trolley operator is closing the door, Valiant starts to fold the check. But in the next shot, he starts folding it again the same way. (00:09:35)
Other mistake: When Eddie Valiant gets thrown out of the Ink and Paint Club, he is already starting to go through the air as the gorilla moves his hands to throw him. (00:21:20)
Continuity mistake: In the scene where Hoskins is washing his clothes and hiding Roger notice that the weasel talking is holding a gun. Hoskins puts a bar of soap in his mouth and the gun disappears. Then when he comes back to Hoskins the gun reappears. (00:42:15)
Continuity mistake: In the scene where the weasels are in Eddie's office, when the other four weasels see their leader falling down the stairs, Stupid (the fat weasel) closes the middle drawer on the filing cabinet. In the next shot the drawer is open. (00:42:20)
Continuity mistake: In the scene where the gorilla is throwing Hoskins out of the club notice he is facing forward but when he lands in the trash he lands on his back. (00:21:20)
Continuity mistake: At Valiant' office notice the bottle of whiskey on the table, right before he examines the pictures of Jessica and Acme, the bottle is about almost full. But in the next scene after he finds out that Roger is there he sits down and you hear him pour himself a drink. In the next shot the bottle is almost empty and he is holding a glass that only holds about a mouthful of whiskey. How could he pour that little amount of whiskey and lose that much? (00:36:00)
Continuity mistake: In the scene at Valiant' office, Roger starts reading the letter but when he jumps off the bed in front of Valiant, the letter disappears. (00:38:35)
Continuity mistake: Mr. Maroon talks Valiant into working for him, he has his head tilted sideways. A brief back shot shows the head straight, but the immediate front angle shows it tilted again. (00:06:55)
Continuity mistake: When Eddie is on Maroon's office pouring himself some bourbon, Dumbo shows up and scares Eddie, who throws himself on the ground. The camera then shows him and his empty glass, and the ground is dry. Where did the bourbon go? (00:08:00)
Revealing mistake: When Eddy is fighting Judge Doom, Eddy is holding a giant cartoon magnet. He then attracts Judge Doom's sword and when Eddy drops the magnet it is attracted to a steel drum. If you look at the bottom of the drum you can see two strings on the bottom of the drum as it moves towards Bob Hoskins. (01:27:10)
Other mistake: At the beginning of the movie, when Roger is begging the director to give him another chance and keeps grabbing the bottom of the director's jacket that is in the director's hand, at one point the bottom of the jacket leaps into Roger's hand before he actually grabs it. (00:05:05)
Deliberate mistake: Before Eddie turns on the band machine in the factory, we see Smart Guy holding a real gun. Three shots later, when the weasel is backing away in surprise, he is holding a toon gun, which later switches back to a real gun. (01:23:30)
Answer: Valiant also shares his name with Arthurian comic strip hero Prince Valiant, who wields a singing sword, Flamberge.