David Letterman came out of his retirement from late night comedy to stop by Jimmy Kimmel Live! and couldn’t help but seize the opportunity to tease the current late night stars. While Letterman was ostensibly on the show to discuss receiving the Mark Twain Prize for American Humor as well as the Netflix show he is developing, he also had to do a little explaining about a certain horse. Last week, Conan O’Brien appeared on Stephen Colbert’s Late Show to complain that when he started on The Tonight Show, Letterman had sent him a horse as a congratulatory gift.