MSNBC host Rachel Maddow has been on a tour of late-night shows, where the Rhodes Scholar explains the massive flaws in our political and economic systems. Another common duty: Answering questions about Keith Olbermann.

These tend to be of the What Is The Deal With That Guy variety; David Letterman's focus on the Late Show last night was on the Countdown host's massively inflated cranium. As always, Maddow walked a delicate line between polite laughter and not publicly mocking her benefactor and liberal fellow-traveler.

Not that Letterman made it easy: He caught the Rachel Maddow Show host off-guard by quickly dropping his Olbermann needling at the start of the show only to resurrect it out of the blue at the end. One can only not laugh at Keith Olbermann for so long. See clip above.