Is the same person perceived as more dangerous if the perceiver is induced to think about Arab and Muslim categories versus no category? Using the shooter paradigm, this study investigated the effects of the accessibility of ethnic (Arab) versus religious (Muslim) categories versus no category on spontaneous aggressive responses toward a target with an ambiguous appearance. Results demonstrated that shooting reactions toward armed targets were faster than non-shooting reactions toward unarmed targets, especially if the target was a man. Despite these main effects, participants made faster decisions to shoot an ambiguous armed target if primed with the category Arab or Muslim (versus no category priming). The findings indicate that the mere priming of these social categories is sufficient to facilitate aggressive responses, even if the targets themselves are ambiguous. Copyright © 2012 John Wiley & Sons, Ltd.