  As robots are increasingly endowed with social and communicative
capabilities, they will interact with humans in more settings, both
collaborative and competitive. We explore human-robot relationships in the
context of a competitive Stackelberg Security Game. We vary humanoid robot
expressive language (in the form of "encouraging" or "discouraging" verbal
commentary) and measure the impact on participants' rationality, strategy
prioritization, mood, and perceptions of the robot. We learn that a robot
opponent that makes discouraging comments causes a human to play a game less
rationally and to perceive the robot more negatively. We also contribute a
simple open source Natural Language Processing framework for generating
expressive sentences, which was used to generate the speech of our autonomous
social robot.
