The entire film from minute 10 to minute 20 is reversed, as revealed by (1) the backwards lettering in the London establishing shot and the signs visible in the back window during Cliff's taxi ride with his father, (2) male characters shaking hands with their left hands, and (3) breast pocket handkerchiefs appearing on the wearer's right side in this section and the traditional left side in all other parts of the film. It is first noticeable when the taxi pulls up to the Everett's apartment - the lettering of "36 Sutton Place" on the awning is reversed. It ends when Cliff Barton leaves Mr. Carew's office in London. It's as if the second reel of the film was printed reversed for some reason.
Furthermore, at around minute 35, as Ms. Mueller plays the piano, it appears that her heavy bass chords are struck at the treble (right) end of the keyboard.
When Mrs. Salt meets with Mrs. Linka in the latter's hotel room in New York, the movements of Mrs. Salt's mouth do not match the words she is speaking in one short segment of their dialogue.