Factual error: When Stephanie gets in the back of the zoo wagon, she discovers a zebra back there. Then all of a sudden the zebra toots and the flames go way out of the back of the trailer. In real life that wouldn't happen because the gas doesn't come out of your rear end fast enough to have that happen.
Continuity mistake: In the pet shop, Gordon gets all wrapped up with plastic wrap. Just a few short scenes later it's gone. There's no way he could have gotten himself out of it in that amount of time. Also, the "plastic" fishbowl shatters - plastic fishbowls like that are not that rigid and would not break like that. Add to that the "piranha" tank is obviously a bubble line at the back of the tank - you can see the bubbles come up when they reach the fishnet in.
Continuity mistake: During the end of the movie, spot is in the park again, and when he looks at the bad guys, he has a collar on and then when he looks back, it is off. This happens for a minute or two.
Continuity mistake: Towards the end, the mail truck has a reflector hanging outward on the driver side. Later scenes, it's back in place.
Continuity mistake: When the boy gets a call from his mom, she is far away from the truck. When it spits mud up, she is right next to it.
Continuity mistake: In the opening sequence, the driver's door on the mail truck is wide open. When the protagonist arrives at his destination a moment later, the door is closed.