Actors know that pulling off a role as the opposite sex will really impress the audience. As far as appearances go, it's pretty easy with proper hair and makeup -and sometimes a good shave. That just goes to show that there are more differences in appearance among men and women than between men and women. But acting the part when you don't have the experience of being the opposite sex shows some real acting chops. I've tried voice acting as a man and couldn't get rid of the feminine accent. But these actors did it, and did it better than we expected at the time. See a gallery of 13 opposite sex roles at TVOM.