As fans of “The Walking Dead” know, one of the pleasures of watching the show is pointing out its various inconsistencies. It’s a show that practically invites nitpicking. (I mean, is it really that easy to decapitate the undead? Don’t zombies ever starve? And just how is the electricity still working at this point, a year or so into the zombie apocalypse?) On Thursday night, Conan O’Brien got the chance to do what millions of Internet commenters and fanboys across the globe would like to do: He grilled Robert Kirkman, the author of the original comic books and an executive producer on the series, about the many things on “The Walking Dead” that don’t completely make sense.