Continuity mistake: When the frozen Fairy shatters, part of her legs and waist remain standing. When David is touched by the alien, half a second later, those remains are completely different.
Continuity mistake: When stranding David, the mother cries, "I gotta leave", and then her hand swaps from resting on his shoulder with extended fingers, to clutching his shoulder, between shots.
Continuity mistake: About to strand David, his mother stops the car for a brief second. When she continues driving, a large amount of debris has appeared on the road.
Continuity mistake: When David is drawing and his mother arrives, the position of the chair changes between shots.
Continuity mistake: While being operated, the way David's sweatshirt is folded differs between the front and back shot, when he says, "Mom, it doesn't hurt."
Chosen answer: His license is a tracking device. By removing it, he's preventing the authorities from easily tracking him.