Revealing mistake: In the swimming pool scene, when David is sitting at the bottom of the pool, you can clearly see a scab on one of his knees. (00:43:00)
Continuity mistake: The poem displayed in Dr. Know's booth and the one on the door in Manhattan are slightly different. Dr. Know displays the line "waters and the wild" whereas the poem on the door read "waters of the wild." (01:26:30 - 01:34:10)
Continuity mistake: When we see the chef mecha in the cage, he has a hat on, and it is a permanent part of his head. But earlier when he was searching for an eye in the pile of stuff, he doesn't even have it on. (00:58:00 - 01:27:20)
Continuity mistake: In the scene where Martin is convincing David to go cut a lock of Monica's hair, watch David's top pajama button. When you see David head on, it's unbuttoned, but when seen from the side, it's buttoned. (00:39:13)
Chosen answer: His license is a tracking device. By removing it, he's preventing the authorities from easily tracking him.