The matting process cuts off Roger's whiskers in most scenes. Sometimes you see the tips of the whiskers silhouetted against an arm or an ear, but the space in between is blank. (Fixed in the 2003 Vista Series DVD, where the full whiskers are present throughout the movie.)
Many of the liquor and beer bottles were of an incorrect shape or had labels that were not used for another couple of decades. Examples being the Wild Turkey he shoots with the tomahawk bullet and the Budweiser behind the bar when Doom tries to apprehend Roger.
During the scene where the taxi is chased by the weasels, the taxi springs into the air to mount a road on a bridge. For a short clip, yellow road stripping can be seen. Los Angeles and California, while having double striping down the center used white paint until the early 1960s when they introduced yellow. Dashed center lines would have remained white until the 70s.
In the scene where the taxi is about to mount the road on the bridge, a modern day lamp post can be seen. While this design 'may' have been around in 1947, it would have been brand new, and unlikely to have been placed on an obscure road.
As Eddie Valiant drags R.K. Maroon to the Movieola, Maroon says "I'm a cartoon maker, not a murderer." The close-up of Eddie and Maroon at the Movieola occurs just as Maroon is saying "murderer", but he is not speaking.
When Eddie Valient is first leaving R. K. Maroon's office, he looks to see the man playing the saxophone for the Fantasia (1940) brooms. Yet, the sax player is not moving his fingers, but merely holding the sax. He is not playing it at all, just moving around.
When Eddie Valiant sits on the back of the trolley car, the overhead power grid is visible and connected to the car. When he gets off, the connector rods are sticking up into thin air with no grid anywhere.
When the weasels enters Eddie Valiant's apartment to find Roger, the weasel known as Smart-Ass holds a real gun. When he walks up to Eddie, the gun has a shadow, but Smart-Ass doesn't. In the next shot, he has a shadow as well.
When Maroon is trying to coax Eddie to take the detective job during their first meeting, Eddie goes for the glass whiskey decanter on the right. He pours himself a few sips of whiskey, an amount so small that the bottle's still very full when he puts it down. However, after Dumbo scares him and makes him drop to the floor, you see the whiskey decanter again, now missing a significantly noticeable amount of whiskey.
When Betty Boop talks to Eddie at the club, she sets down her cigarette tray and a "clunk" noise is heard, like it is being set on a table. It then cuts to a longer shot, and there is no tray nor a table to set it on near Betty.
When Eddie and Roger escape from the Weasels in the bar, they run to the Weasels' truck. Roger squeezes through the slot to find Benny and the love letter pops out. You can see a crew member's black gloved hand shove the letter through to Eddie.
After Roger spots the weasels from Eddie's office and goes into a frenzy, he pulls Eddie under the bed because they are cuffed together. You can clearly see the trolley placed under Eddie to make it seem like he was sliding on the floor.
Throughout the movie the streetcar tracks are shown as merely railheads slightly higher than pavement level. All in-street rail requires a flangeway for the wheel flanges that keep the wheels on the track. Typically, grooved rail or girder rail would be used.
During the scene where Eddie Valiant and Roger hides in the secret room in the bar for the first time, Eddie hands Dolores a picture of Acme's will. The picture however is cropped and only shows his pocket with the will in it. Yet from the moment Eddie first notices the will on the picture on the news paper, and until he hands the picture to Dolores, there is no time that he would have had the time to crop the photo. Back in 1947 to crop the image he would have had to re-process the photos from the negatives, and he did not have the time to do so between the two scenes.
Set in 1947, the movie features the Singing Sword bearing the likeness of Frank Sinatra that croons several bars of the Cy Coleman & Carolyn Leigh song "Witchcraft", which wasn't written, and which Sinatra didn't record, until 1957. But that's in our universe; perhaps it was already a big hit in Toon Town, whose residents used Coleman and Leigh as a front to raise some much-needed simoleons by selling the song to Sinatra).
Some of the "toons" living in Toon Town were not created in the real world until after 1947. In the movie's world they were already living in Toon Town, and not "discovered" until 1949, 1953, and the other years when they made their specific debuts.
After Roger blows his nose on the handkerchief, it's obvious R. K. Maroon didn't grab the handkerchief out of his hand. It appears he was reaching down to get the handkerchief. However, Maroon's handkerchief would have presumably been dirtied by Roger's tears and nose blowing. A person would normally try to retrieve such a handkerchief by taking it gingerly by a place presumed to be unspoiled. This reaction is further verified by the fact that Maroon immediately places the handkerchief in the wastebasket.
When Roger Rabbit drinks the whiskey in the bar while being held at the neck by Judge Doom, the Judge briefly lets go of him, but Roger doesn't fall down. (The moment he let go was when Roger swallows the whiskey, so he presumably opened up his hand to allow space for Roger's neck to get bigger when the whiskey is swallowed. However he may have opened his hand too wide or the animation was not successfully drawn to match the hand movement.)
A live-action model was used in the scene in the Ink and Paint club during Jessica's song parts of her were rotoscoped in order to cover the model up. Jessica interacts with Marvin Acme by pinching his cheeks and then taking his handkerchief out of his coat pocket and polishing his head with it. If you look closely, you will see Jessica's hands briefly grow to human proportions as she interacts with Acme. This occurs again when she interacts with Eddie later in the same scene. In fact, there is a tiny glitch in the animation of her hands as they go from rotoscope to animation after she shoves Eddie's hat into his face. Finally, as the camera closes in on Jessica and Eddie in the final moments of the song if you slow down the film speed, you will see Jessica's dress move ahead of her for a few frames to cover the performance model. Again Jessica's hands are rotoscoped as they pull on Eddie's tie.
During Baby Herman's discussion with Eddie outside Eddie's apartment/office, Baby Herman hands Eddie a newspaper. When Eddie first takes the newspaper, just before he turns it over, it is clearly visible that most of the bottom front page (i.e., "below the fold") is blank.
Although the street cars are shown to drive on rails, they are actually decorated buses with rubber tires. This is noticeable through the way they come to a stop: a rail car is unable to stop as abruptly as the cars in the movie, and will not exhibit the typical 'bounce' of a vehicle with tires.
After Maroon takes the wet handkerchief that Roger blew his nose in, he walks to throw it in the trash. As Maroon is walking, the handkerchief should be wet from Roger blowing his nose and crying, but moves as if it were dry.
The goof items below may give away important plot points.
When Roger arrives at the Acme warehouse to save Jessica, he is carrying the real gun that Eddie took from Maroon and subsequently discarded. It becomes a Toon gun during his confrontation with Doom, however.
When Judge Doom is melting, he is standing upright, with his body and clothing melting in a pile on top of itself, but when everyone is examining the 'crazy toon', his clothing is laid out, like he was laying down when he melted.
At the end of the movie Eddie just saves himself from being crushed by the steamroller. After he jumps over the steamroller and kicks Doom to the floor you can still see the steamroller driving away from him and Doom. Then Doom gets up and smacks Eddie to the ground and suddenly the steamroller is coming his way. Somehow it has turned 180 degrees.
It is supposed to be impossible to kill toons any way other than the Dip, yet the weasels die laughing. However, it is stated that the characters *thought* it was impossible to kill a toon. Humans may have been unaware that toons could die from laughter. The Judge does say that the toon weasels' "idiot hyena cousins" died. Alternatively, humans may hire a number of phantom toons, such as Casper the Friendly Ghost, and not consider them quite dead enough. When Smart-Ass falls into the Dip, he is not seen turning into an angel like the other weasels, suggesting his fate to be much more serious.
When Judge Doom removes his glove, he reveals a toon anvil as a hand, which he then changes into a toon buzzsaw. Supposedly, his gloves were to used to hide his "toony" hands. When Doom gets hit by the stream of dip firing out of the machine, his hand is still bare, but this time it's Christopher Lloyd's real, unanimated hand. When he starts melting, the glove's back on.
The shadows "cast" by the cartoon characters often do not match the shadows of the real actors in density and definition. This is especially noticeable when Roger confronts Judge Doom and the weasels at the Acme warehouse.
After the climax, Eddie opens a firewater valve to flush away the dip. He turns the valve clockwise. To open a valve of this type, it must be turned counter-clockwise. Even if this was some special reverse-convention valve, note that Eddie turns it the SAME clockwise direction when closing it moments later.