These are the answers that they rehearse with the candidate so he doesn’t sound like an idiot:

Sen. Barack Obama’s pitch perfect response regarding the announcement of an impending birth in the Palin family (“my mother had me when she was 18”) was not without a series of edits and rehearsals, according to some Obama insiders.
“For tough questions we know he will get to questions we plant with reporters that we want asked, [senior campaign staff] will rehearse [Obama’s] answer with him.”
The goal: to get his inflection and tone, as well as the content, just right.
“After he flubbed the hypothetical question about his own daughter’s pregnancy, the campaign has worked with him to avoid what appear to be insensitive or unthoughtful answers,” says an Obama Senate staffer.

Now when you hear Obama respond to a question with a good answer, you know that he’s had time to rehearse it.