There is some confusion over the POV when Dr. Fennick grabs the neck of Doctor Norton when he kills him. The camera's view is out of focus, as if it's showing what Dr. Norton sees as he's being strangled, but it looks like Fennick is actually strangling someone else off to the left side of the camera, which would not be how Dr. Norton would see it.
In his closing segment, Hitchcock pronounces the the name of the Ray Milland character "Dr. Fenwick" rather than "Fennick." The other characters use the correct pronunciation during the story itself.
"Fenwick" would be pronounced with a silent "W," as in "Greenwich." The actors in the story were all on the same page, so to speak, but Hitchcock, who would have recorded his opening and closing segments apart from the main production, was on another.