A conversational robot can take on different personas that have more or less common ground with users. With more common ground, communication is more efficient. We studied this process experimentally. A "male" or "female" robot queried users about romantic dating norms. We expected users to assume a female robot knows more about dating norms than a male robot. If so, users should describe dating norms efficiently to a female robot but elaborate on these norms to a male robot. Users, especially women discussing norms for women, used more words explaining dating norms to the male robot than to a female robot. We suggest that through simple changes in a robot's persona, we can elicit different levels of information from users-less if the robot's goal is efficient speech, more, if the robot's goal is redundancy, description, explanation, and elaboration.