Act III-When Mrs. Thorne is dropped off at the airport. She has finished buying a magazine and Mr Creepy is at the book rack. Some titles of the books on the rack are legible-Two Couches & Harvest on the Don, in the very first shot of him. The subsequent three shots of him by the book rack, the books are shaded or blurred.
The shot at the airport of the taxi pulling to the curb behind the bus seen in the middle of Act I is the very same shot used at the beginning of Act III.
At the beginning the Doctor is mystified that the patient Vincent has brought in has such a strange x-ray. It's inconceivable that the Doctor hadn't noticed that the patient (who is unconscious not dead) also didn't have a heartbeat or a blood pressure.
In reply to a compliment about being like "the 7th Cavalry", David Vincent pronounces the unit's name incorrectly as "the 7th Calvary".
When the doctor goes to check on the Invader patient, the alien uses the familiar disc device to kill him. Even if David didn't expect the Invader to regain consciousness, he should searched his clothes before taking him to the doctor, if for no other reason to finally have the advanced technology that proves the Invaders exist.