This is the original casting call ad that Letterman posted in The New York Times. Ahh, such humble beginnings...

HAVE YOU TAUGHT YOUR PET TO DO SOMETHING ODD?
Late Night with David Letterman on NBC will feature pets who have been trained to do unusual things. Pets must be amateur & owners must be willing to appear w/them at auditions & on the show. To audition your pet, please call Chris 10-5pm: 212-xxx-xxxx
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