Michelle Obama surprises White House tourists

White House tourists had an unexpected visitor on Thursday morning. First Lady Michelle Obama and first dog Bo unexpectedly dropped by some visitors on White House tours.

With Bo at her side, the first lady stood and greeted visitors as they were ushered through the White House public viewing rooms. She hugged each passer by, including many elderly women in wheelchairs. One tourist broke into tears as she so overwhelmed with emotion at the shock of seeing the first lady. (watch video at left).

To a group of school children, Mrs. Obama joked that there would be a test on what they learned before they left.

According to the AP, she said "You don't get out of the house unless you pass it." Witnessing the serious faces, she reassured the students. "I'm kidding," she said.

The first lady announced her plans via a tweet and invited people to watch it live on the White House website.

For more than an hour, the first lady greeted and spoke to about sightseeing, food and her "Let's Move" campaign.

Tickets for self-guided tours are free and obtained through members of Congress.