Following up on our follow-up about Katie Couric's appearance on Wednesday's Late Show with David Letterman, Couric called in to last night's show to discuss the topic Letterman "forgot to ask" — the day Sen. John McCain canceled on Dave only to show up with Katie.

"I was all prepped to chat with you about this and you had, like, brain synapses misfiring," said Couric. Says Letterman, "I think you were in on this, I think you were a part of this."

So when did Couric find out about the cancellation? "I had no idea until you had a little cow on the air with Keith Olbermann," she said. "Then you did that creepy 'Big Brother' thing by stealing our video."

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