When Blunt, 32, appeared on the show, she said she knew about American history, saying, "I know more about the constitution and government than most Americans."
DeGeneres, 57, then convinced the "Edge of Tomorrow" actress to dress up like Lady Liberty and sing patriotic songs in celebration of her new status, reported People Magazine.
"I feel like this is going to get me in trouble," Blunt said nervously.
As the actress attempted to sing along to "Yankee Doodle Dandy", a man dressed as Uncle Sam walked up to her and shouted in her face. Blunt screamed back in his face before falling into a pit of laughter.