The Pokemon film is out this weekend, on a wave of generally positive reviews.
But one scene – that is featured heavily in the trailers – was the result of Letterman fighting hard with bosses at The Pokemon Company.
The creature in question? Mr Mime.
Recalling his initial idea, he told IGN: “I thought it would be really funny if we played that classic film noir detective interrogation scene, but with Mr Mime.
“A classic police interrogation scene ripped out of every detective movie I could think of, but flipped on its head.
“Because the uncooperative informant that they’re interviewing happens to be a mime.”
He went on: “I thought no way in a million years would (the scene) work. Honestly. It was so weird.
“I wanted to cut it at one point, because I was like this can’t possibly work. It’s insane.
“I went to The Pokémon Company. I was like ‘I have this idea for this scene, and it requires realising Mr Mime photoreal into the live-action world’.
“They thought about it, and… they literally looked at me like, ‘yeah you don’t wanna do that. That’s not gonna work. That’s gonna be too weird. That’s gonna be creepy’.
“It came to the point where I literally had to ask the President of the whole Pokemon Company, Ishihara-san.
“I gave him the whole pitch, and he started laughing, and he’s like, ‘okay, give it a shot’.”
Letterman called the scene “the most awkward, weird thing to shoot”.
Nonetheless, it made it into the finished cut – and multiple trailers – so presumably was worth all the effort.
Detective Pikachu stars Justice Smith as the human lead, with Ryan Reynolds voicing the titular iconic Pokemon.
Detective Pikachu is out tomorrow.