Continuity mistake: It's shown in many scenes that the robot Gallaxar sends isn't particularly quick moving when it walks. But when it's chasing Ginormica around the city, even though Ginormica is sprinting away, it can catch her far more quickly than its speed would allow. It doesn't suddenly speed up - in the shots when the camera focuses on the robot again, you can still see it moving slowly.
Factual error: The size of the shadow of an object depends upon its distance from the light source, not the surface it falls upon. Lifting the cutout of the bird a few inches closer to the sun as they do would make absolutely no difference to the size of its shadow, yet it quadruples in size.
Factual error: Johnny shows Mavis the sunrise by keeping her back in the shadows. But if your whole body is in an object's shadow then you can't see the light source. The rising sun is reflected dead center in Mavis' eyes, which means the sunlight is touching her, which means she ought to be on fire.
Continuity mistake: Lady is put in her bed and the master leaves the kitchen but he goes back in and puts a newspaper on the floor and leaves again but Lady gets out of her bed so the master comes back once more and puts her back in her bed but the newspaper on the floor has vanished.
Continuity mistake: The scene where Col. Hathi inspects his troops, he leans on his stick and it breaks. However, in the next scenes, the stick you see is sometimes broken and sometimes it is still complete.
Continuity mistake: When Dr. Doppler and Jim first observe their ship, Dr. Doppler is right next to Jim when he points it out. When the shot changes to a long shot, they're much farther apart. (00:16:55)
Revealing mistake: In the scene where Rocky and Bullwinkle are walking through the university with Kenan and Kel (right before they come across the anti-moose protest), Kel's right arm passes through Rocky's left several times.
Continuity mistake: When Tiger and Fievel are doing their musical piece, Tiger wipes off the mirror and they appear the same size. When he lays out in front of the mirror, singing the line "We'll be there to pick each other off the floor", he places his head next to the cage bottom, still laying on the floor between them. In the mirror, however, that cage bottom is not reflected at all. (00:57:30)
Continuity mistake: When the Were-Rabbit jumps through the stained glass, the right ear is pointing to both dragon wings. But when the Reverend is telling his tale, the glass break is is pushed way over and the hand print is now where the ear print should be. (00:24:55 - 00:28:15)