The taxi that drops off Albert Sully at the London pub is an American-style car with left-hand drive.
Jesslyn Fax is miscredited at the end as Mr. Willard, rather than Mrs. Willard.
In several scenes, the word "freon" is badly overdubbed with the word "hydro" in a voice totally different than that of the character talking.
The opening credits identity Carroll O'Connor's character as Walter B. Brach. However, the dialogue refers to him repeatedly as Walter G. Brach.
We learn that Napoleon Solo served in the Korean War.
When the guards are struggling with Horth in the hallway, notice the guard on the left as they turn him around. His machine gun is over his shoulder and it bends as it presses against the wall, revealing it to be made of rubber.
While Solo, Kuryakin, Raven, and Horth are spying on a camp from rocks high above, Horth stands up, ready to go, and catches Solo under the chin with his rifle.
When Waverly hands Napoleon the file on Vulcan, they're standing in a corridor. However, in the next closeup shot of the file, a telephone is visible behind the file, as if someone were holding it just above a desk.
In the movie version Thrush is called 'Wasp' but is clearly dubbed over.