The ambulance driver states that he has to go through the Sumner Tunnel to get to Logan Airport. Since 1961, the tunnel going to Logan has been the Callahan tunnel. The Sumner tunnel has been outbound from the airport since 1962.
When Dr. Harris completes an appendectomy, the anesthesiologist reaches for the patient's endotracheal tube, as Dr Harris begins to turn away. When he completes the turn, the anesthesiologist is seen removing a face mask from the patient. There was no time for the anesthesiologist to remove the tube and replace it with the mask.
The MG-B that Dr. Wheeler drives in the opening scene with a tan interior and a black plastic honeycomb grille switches to an earlier model with a black interior and an all chrome grille (noticeable in the scene where the car will not start). When Dr. Wheeler visits the Jefferson Institute, it has switched back to the MG-B with the tan interior and black grille.
In the scene toward the end, where Dr. Susan Wheeler discovers Tom Selleck's body after it has been "harvested" it is Tom himself laying on the table. Later shots show that a dummy with a bad wig has been substituted for the actor.