After Kyle and Tyco leave the shelter and Tyco is pulling kyle on the skateboard, they go from concrete to grass. When kyle is doing the skate tricks it's a normal skateboard, but when they cut to when they leave the concrete to the grass, the wide shots show extra large wheels all of a sudden, such as those used on the off-road skateboards.
In the beginning of the movie when all the children are taking home the free puppies, there are four black puppies and the golden puppy Tyco. It shows all the children taking home the puppies. When four children have picked up the puppies a fifth child comes and picks up a fifth black puppy. Where did this fifth puppy come from?
When Kyle is talking to Emily, getting ready to leave the shelter with Tyco for the first time, in the shots of just his face, his collar is down. But in the shots where it shows him and Emily, his collar is sticking right up.
When Kyle and Tyco win the dog show at the end of the movie, when they cut to Tyco holding the skateboard in his mouth you can tell that it is actually a Styrofoam skateboard.
When Calvin and Emily are playing a video game they are using controllers for a Nintendo 64 system but in a wide shot their is no cartridge in the N64 on the table.
When Tyco is pulling Calvin through the obstacle course, Tyco is seen jumping over an obstacle. The end of his leash is clearly visible with no one holding it. The camera then quickly cuts to Calvin, who is still hanging on to the leash.
When the band is shown playing at the basketball game, it is obvious that they are not really playing.
Most prestigious dog shows require dogs to be purebreds and for owners to be able to provide breeding papers if necessary. Being that many of the dogs appear to be purebreds it would stand to reason that Tyco's breed would be called into question and if Calvin possessed any breeding papers but it is never called into question. If the rules of the dog show did require all dogs competing to be purebred then Tyco and Calvin would have been disqualified from competing.