Sen. Barack Obama got some laughs from an audience in Knoxville, Iowa, Sunday for mocking Republican Mitt Romney.

An undecided voter asked Obama how he differs from Romney. He quipped that the former governor doesn't use "serious" curse words, and added: "I have to tell you, I've used some really harsh curse words, the really good ones, the juicy ones."

Obama goes on to talk about how he is different from Republicans in general. Here's some video:

Romney spokesman Kevin Madden says his boss never said he avoids harsh cuss words, and says "the gov doesn't swear," but quips back:

"Gosh golly, I can't think why Barack Obama thinks using swear words is a presidential quality. Fluency in swearing is for press secretaries who are working with reporters only."

(I'll back Madden up on that point.)

Another questioner asked Obama about personality traits that would help him work with Republicans if he is elected.

He used health care reform as his example, and told the crowd he would have a "big table" with doctors, nurses, patients, administrators, labors, insurance companies and drug companies each getting a chair.

"I'll have the biggest chair because I'll be president, it will be a big comfortable chair," he said, laughing at his own joke.

Further, "It will be on C-Span, and you will be watching the negotiations taking place," he said.

I have a story that went live after midnight from the campaign trail, examining Obama's argument that he is more "normal" than the other candidates since he and his family worried about student loans, college savings and credit card debt a few years ago.

Also worth mentioning, the Richardson campaign announced that that actor Martin Sheen has a "severe, contagious cold" and his doctor has forbidden him from flying to Iowa to stump for the New Mexico governor.

Sheen said in a statement he is "deeply sorry" and, "I believe with all of my heart that he is the candidate we must elect as the next President of the United States. At this critical time in our nation's history, Bill Richardson is the one person with the experience and vision to rebuild our reputation and alliances abroad and improve the lives of all Americans here at home. I hope that the people of Iowa will forgive me for not being able to fulfill my commitment, and I urge them to caucus for Governor Richardson on January 3rd."

-- Christina Bellantoni, national political reporter, The Washington Times