It's touching that Shelley Duvall used to call Altman "Pirate", and weedy, boozy testimonials from coconspirators Tim Robbins and Michael Murphy are fun but hardly surprising (neither are their unpleasant, ugly flipsides); and Altman's alluded-to affair with Faye Dunaway has apparently been a matter of public record since at least 1989—though if this comes as news to you, as it did to me, you're going to want to take a minute to really fully consider the implications here, because seriously, what?—so in looking for something new to post here we turn to Dana Stevens, at Slate, who has already taken the trouble of typing up the section of the book in which Robert Altman tattoos Harry Truman's dog.
Yes, it turns out that, after getting out of World War Two, Bob tried his hands in the dog-tattooing racket, inscribing some identifying marks on the haunch of an unloved Truman family puppy ("Truman had this dog he didn’t even care about, a little dog of some kind. They sent it over to us and we tattooed it.").
Given the timing of Altman's discharge from the armed services, the dog would presumably have been Feller, a Cocker Spaniel. And Robert Altman tattooed him. There you have it.
This is not the only time a major American filmmaker has tattooed the a presidential pet, of course: to guard against espionage during the Second World War, William Wyler was assigned the task of tattooing Fala, Franklin Roosevelt's terrier, in between directing newsreels; in 1977, George Roy Hill did an anchor on Liberty's left foreleg (at Betty Ford's request). And in 1995, Mary Harron and Socks the cat got matching tramp stamps.