On their first morning in London, McKenna leaves a taxi and walks down a quiet residential street and stops at the next corner. Four or five camera shots were taken as he slowly walked down the street. In the first three or four shots the shadow of the buildings along the block extended across the sidewalk to about three feet into the street. But in the final scene at the corner the shadows were gone.
The Camden Town scene: As Dr. McKenna walks along the deserted street, a figure (Ambrose Chappell Jr.) turns the corner and walks behind him, down the center of the pavement (seen from Dr. Mckenna's POV). The camera cuts to view further along the street, with both characters in shot, but Ambrose Chappell has "jumped" to the edge of the pavement.
Prior to Dr. McKenna and Jo enter Ambrose Chapel, there is a white stain on Dr. McKenna's left shoulder, apparently from the struggle at the taxidermist. As soon as Dr. McKenna enters the chapel, the stain disappears, then reappears after they take their place in the chapel.
When the two men and the woman are discussing the music arrangements with the shot to be fired at Ambrose Chapel, the cigarette she is smoking is much smaller than the one that she extinguishes before she and the men go to leave the room.
When Jo, who is in a hurry to get to Albert Hall, gets out of the taxi, she quickly walks past a man and woman wearing black and brown coats. When Jo soon arrives at Albert Hall, the same couple is ahead of her again.
In the opening scene on the bus, there is a pretty brunette and a pretty blonde sitting in the seat directly in front of Jo. After Hank accidentally pulls the Arab woman's veil off, and goes back to his mother, the two women just disappear in a flash, allowing Louis Bernard to be able to sit down and "interrogate" Jo and Ben.
When Louis Bernard is stabbed from behind, the assassin hits him just below the neck. When Bernard drags himself along in the next shot, the knife can be seen sticking in his back much lower, between the shoulder blades.
During the interrogation after the Albert Hall assassination attempt, the telephone used is an obvious Western Electric American-made phone instead of a British-manufactured telephone - betraying the fact that the interiors for this picture were shot in Hollywood.
The Doctor told Louis Bernard, when they first met on the bus, that they "limped" in from Paris by way of Lisbon, Rome and Casablanca.. From Paris, it would have been a straight shot by way of Lisbon and Casablanca, but Rome would have been extremely way out of their way by a far distance.
After Luis Bernard has died in McKenna's arms, McKenna finds the knife lying under the body. The blade has no blood stains on it. Furthermore, if the knife would fall out of the wound so easily, it hardly could have been deep enough as to be lethal.
Ben climbs up the bell rope and out the top of the bell tower to escape the chapel. A bell in such a small tower could not possibly be heavy enough to counterbalance Ben's body weight. Therefore Ben would pull the bell to its limit while climbing, and the bell would not ring repeatedly as he climbs the rope. And when Ben pulls the rope taut so that he can rappel down the roof, the bell rings twice more.
When the McKennas are riding to their hotel in the horse-drawn wagon after getting off the bus, the shadows are mismatched between the foreground and the back-projected scene. In the foreground, the shadows are on the left of the characters, as if the sun is on the right of the frame; in the back-projection, the shadows are on the right of the cars, as if the sun is on the left of the frame.
In the climactic scene at the Albert Hall concert, when the cymbalist stands, turns and grabs his cymbals, the timpanist beside him is playing, but is clearly not hitting the drums. Also, the timpanist is not the same person who was playing (correctly) during the title sequence.
During the initial bus ride when the driver slams on the brakes, Hank falls backward, however, if the bus were actually in motion, his inertia would have carried him forward, toward the front of the bus.