  Human collaborators coordinate effectively their actions through both verbal
and non-verbal communication. We believe that the the same should hold for
human-robot teams. We propose a formalism that enables a robot to decide
optimally between doing a task and issuing an utterance. We focus on two types
of utterances: verbal commands, where the robot expresses how it wants its
human teammate to behave, and state-conveying actions, where the robot explains
why it is behaving this way. Human subject experiments show that enabling the
robot to issue verbal commands is the most effective form of communicating
objectives, while retaining user trust in the robot. Communicating why
information should be done judiciously, since many participants questioned the
truthfulness of the robot statements.
