Continuity mistake: After failing to catch Sassy, who went down the waterfall, Shadow and Chance are walking by the river bank. In one shot, Shadow's fur is wet, then dry, then wet again.
Continuity mistake: Following Chance's run-in with the porcupine: Right after Animal Control pulled the needles out of his face/snout, he was visibly wounded, with giant red makings which appear on the right side of his face. Then, while the 3 pets are looking down at their hometown which they just realised is only a little distance from where they are (Sassy had just pointed this out to the dogs), those red wounds are now on the left side of Chance's face. Then, by the end of movie the same markings mysteriously disappear and are completely gone in the final scene.
Continuity mistake: Shadow is noticeably played by a different dog after he and the others arrive at the pound. The tell is the second dog has large black markings under his eyes, while the one seen earlier in the film does not.
Continuity mistake: At the mealtime in the kitchen, Sassy is appearing to be Siamese but seconds later she now looks like a Himalayan, which is her real breed in the movie.
Continuity mistake: During the first night when the pets hear animal noises and are scared, there are at least two angles when you can see it was shot during the day. It is dark in the other shots.
