Other mistake: When Martha May is getting ready to put up her lights with the cannon, she pulls a charging handle, and starts firing. If you watch closely, you see a lit string of lights come out, but the spool that they're on isn't moving, or lit up. Then after all of the lights are out, it still fires several more times (watch the aiming indicator- it continues to flash with the sound).
Other mistake: When Hallee Hirsh 's name appears in the credits, a kid on a scooter moves across the screen, and he looks into the camera. (00:00:35)