Richard P. Feynman to Dr. and Mrs. Herman F. Davis, November 29, 1965 / Jack Liberman to Richard P. Feynman, October 31, 1965 / Richard P. Feynman to Jack Liberman, November 30, 1965 / Richard P. Feynman to P. Paelinck, November 24, 1965 by Richard P. Feynman narrated by Richard Poe / Jack Liberman narrated by Johanna Parker