Lay theories or assumptions about nonhuman animal mentality undoubtedly influence relations between people and companion animals. In two experiments respondents gave their impressions of the mental and motivational bases of companion animal social behavior through measures of causal attribution. When gauged against the matched actions of a boy, as in the first experiment, respondents attributed a dog's playing (good behavior) to internal, dispositional factors buta dog's biting (bad behavior) to external, situational factors. A second experiment that focused on a dog's bite revealed clear attributional process on the part of observers. Higher ratings of a dog as the cause of a victim's distress predicted higher ratings of a dog's guilt. Higher ratings that a dog had an excuse predicted stronger recommendations for forgiveness. Individual differences in seeing the actor as a "good dog" systematically predicted judgments of severity of the outcome and recommendations for punishment. Discussion of these attributional findings referred to tolerance for companion animal misbehavior and relinquishment decisions. This article illustrates the utility of causal attribution as a tool for the study of popular conceptions of nonhuman animal mind and behavior.