Trivia: The scene with Peter Sellers and Sterling Hayden was all adlibbed. Only Hayden had learned his lines, but Sellers did not and all his lines were made up on the spot. One only has to look at Hayden's face that he has no idea what is coming next.
Suggested correction: There is no evidence that any of the scenes or dialogue between Sellers and Hayden was unscripted or ad-libbed at the time of shooting. Sellers was allowed by Kubrick to ad lib during rehearsals, and some of these were incorporated into the screenplay, but all the actors followed the script during shooting.