How much of Stephen Colbert's reaction to Jane Fonda was canned?

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This week, Jane Fonda sat the lap of Stephen Colbert and kissed him with seeming passion and reality. He seemed to squirm visibly (at least less than the interview with Bill O'Reily). How much of his response was canned (pre-scripted) and how much of it was real? He seems to be an expert at making people guess at the sincerity of his reactions.