Before Charlie goes to heaven, his pocket watch strap is red. When Charlie is on the dock right before he gets hit by the car, as Killer is trying to tie the blindfold on a singing Charlie, you see that Charlie's pocket watch strap is blue for that shot, then goes back to red the next.
When King Gator is swimming past Anne-Marie with Charlie on his belly, Charlie helps her up and she sits in his lap. Then when she tells him she doesn't feel good, she is sitting beside him. But from the rear view she is sitting on Charlie's lap again.
When Charlie is in dog heaven he is getting his hand stamped for the life book. The pages are different in two shots.
Just before his death Charlie gets from Carface a gold watch but it is silver. When Charlie is blindfolded the watch is gold.
In the abandoned church that Flo and her puppies live in there is a spiral staircase. It ascends clockwise in almost every scene, except when Charlie is looking up at Anne-Marie.
Despite Charlie being hit by a car pushed deliberately by Carface only the car is seen plunging into the water. This was probably due to the fact that seeing Charlie getting killed would be to dark for a kid's film.
After Itchy asks for directions to 402 Maple St. from another dog, he runs down a street that leads off-screen, but he disappears from the screen before he leaves it.
When Charlie fights with Carface in the abandoned ship, as he looks down at Anne-Marie, the water caustics reflected beneath the ledge are superimposed over Charlie's head.
At the very end, when Annabelle (the pink whippet) is taking Charlie back up to Heaven, Charlie has his blue pocket-watch again (the one he lost in the lake) and their lips are moving yet, they aren't talking. This is because they re-used the beginning of the "Let Me Be Surprised" scene.
Charlie brings pizza to Flo and her pups. Pizza would have been unknown in New Orleans in 1939. It did not become popular all over the United States until after World War II.
When Carface discovers Anne-Marie is gone, he's riding a very crudely made vehicle simulator. At one point, he squeezes the horn on the side, which quite visibly honks, but no sound comes out.
When Itchy repeats the line "402 Maple" after Flo, his mouth doesn't move when he says it.
When Charlie is killed the first time by the car it is pushed down a hill. There are no hills in New Orleans.
Itchy claims Tibet is a city but Tibet is actually a country in China.