16x21 - Late Show with David Letterman

Dave presents the (fake) opening credits of the second presidential debate, which closely resemble Magnum P.I.; Debra Messing plugs "The Starter Wife" and takes a jab at Sarah Palin; Alan's tour of the Late Show control room is sabotaged; Alianca da Terra founder John Carter discusses the plight of the Amazon rainforest; Tegan and Sara performed "Call It Off."