Revealing mistake: When E.B. is running by the Hollywood sign and we see his shadow on the sign, at one point the shadow doesn't touch the ground when it should. It hovers.
Visible crew/equipment: When James Marsden arrives at the house he is watching, he hurriedly opens the door and the camera pushes in on him. The reflection of a crew member can be seen in the left window. It's clear enough you can see the person turn their head.
Answer: Phone.