In a note from Gene Wilder to director Mel Stuart, Wilder pitches that scene in great detail, saying it's important "because from that time on, no one will know if I'm lying or telling the truth."
Wilder also had a great deal to say about the first few sketches of the costume that Wonka wears, calling them "lovely" but stating that he doesn't "think of Willy as an eccentric who holds on to his 1912 Dandy's Sunday suit and wears it in 1970, but rather just as an eccentric," and that he's "part of this world, part of another" (which may be the perfect way to describe Gene Wilder).
The actor even asked for a few changes to the costume: "I love the main thing -- the velvet jacket -- and I mean to show by my sketch the exact same color. But I've added two large pockets to take away from the svelt, feminine line ... The hat is terrific, but making it 2 inches shorter would make it more special."
Wilder's portrayal of Wonka -- his mastery of tongue-twisting lines and the ever-present glint in his eye -- is nothing short of genius, so it's interesting to see the input he had on the character.
The note and more can be found in Wilder's memoir, "Kiss Me Like A Stranger." The letter addressing the sketches is from the "Willy Wonka & the Chocolate Factory" 40th Anniversary Collector's Edition boxset. You can read them both over on Letters of Note.
[via Letters of Note]