After Michael dodges the reindeer and dives off of his bicycle with his back to the camera, one shoulder of the actor's (or stunt double's) hoodie is covered in leaves and twigs, and his other shoulder is clean. However, when the camera angle changes, his previously clean shoulder is now covered in leaves.
It's readily apparent that the remote control airplane they fly at the beginning won't fit in the compact family car (or its trunk). In the subsequent scene it's no longer visible.