_Planet of the Apes_ (filmed in 1967) obviously has some Twainian themes.
Today I was pleased to discover footage of an actor playing Dr. Zeus (or
one of his triumvirate) reading Justin Kaplan's _Mr Clemens and Mark Twain_
(which had just been published), while he was resting off-set between
scenes. See attached pic.

The footage is a few seconds long and appears in actor Roddy McDowall's
'home movies' that he made while shooting the film. See 3:10–4:30 at
https://youtu.be/CNGbQVXNP_I

-TR