The roads, streets, etc. change from dry to wet to dry in the same scene.
When Buddy first jumped through Josh's bedroom window, into Josh's bedroom, Josh was at a desk, reading online. In all scenes thereafter, the desk is replaced with a small chest.
Before Norm chases Buddy and the kid, he slips in the mud. When he climbs into his truck immediately afterwards, his back is dry and free of mud.
In the final basketball game, Josh's hair is down over his face at the start, then gelled back, and then back down again.
When the referee slips in the puddle of drool from Buddy in the last game, he never cleans it up, yet its cleaned up in the next shot.
During the first game against the Spokane Warriors, As soon as the tip-off is about to begin, you can clearly see the scoreboard which reads 20:00. The correct period time for high school basketball is 8:00.
While there may be no rule specifically stating that a dog can't play, interscholastic leagues do have stringent eligibility requirements, including being a student of sound academic standing.
When Bud makes his two free-throws near the end of the final game, he clearly jumps across the free-throw line before the ball hits the basket. In basketball, the shooter can not step across the free-throw line until the ball touches the rim. In both cases, neither free-throw should have counted.
In the second game, the scoreboard is shown as being 15:00 left in the third of four quarters. It is obscene to think that a bunch of kids would be playing 50% longer games than college teams (two 20 minute halves) or 25% more than NBA teams (four 12 minute quarters).
Just before Josh discovers Buddy can play basketball, Buddy holds the ball in his teeth which is obviously flat. When Josh throws the ball to Buddy it is fully inflated. During this time, there was a scene change, because the basketball bounced high in the air, but in slow motion, which means the basketball was changed after Buddy tried to grab the basketball, out from Josh's arms.
Additional Fact: While Josh cleaned Buddy, Josh was wearing a yellow rain suit and when Josh was started drying Buddy, with a towel, the yellow rain suit is no longer on Josh. That was another scene change. Josh was wearing a yellow rain suit, as he started to clean Buddy. As Josh was completing, with drying Buddy, with a towel, Josh was no longer wearing a yellow rain suit.
When Snively is chasing Josh with his truck, the first part that flies out from under the truck after he crashes through the Fernfield sign is the driveshaft. As the preceding scene clearly shows this as a 2-wheel-drive truck, without the driveshaft it is impossible for the truck to accelerate under engine power. It could've possibly coasted faster given the slight downhill grade, but the truck is clearly shown accelerating out of control off the dock.
When Buddy's owner chases Buddy and Josh, numerous shots of him behind the wheel clearly show the transmission lever in "park".
When Snively is chasing Josh and Buddy through the park in his pickup, you would not be likely to see the amount of parts fall out from under the truck because Snively was trying to apply the brakes. None of the parts had anything do with the braking system. If the brakes had failed, you would have seen brake fluid shooting out the bottom of the truck.
It is highly unlikely that the painters would leave open cans of paint on a ladder then leave for the day. They would begin to dry out and be unusable the next time the painters turned up.
When the kids leave school for the Christmas break, the trees are still changing colors in autumn. There would be no leaves on the trees by Christmas in Washington State.
When Buddy runs into the gym in slow motion, a person (presumably his trainer) can be seen running behind him for a split second.
The movie is set in Washington State, but a lot of cars have British Columbia license plates on them.