In 2014, Russia denied that its military was assisting separatists in eastern Ukraine, despite overwhelming evidence. Why do countries bother to deny hostile actions like this even when they are obvious? Scholars have argued that making hostile actions covert can reduce pressure on the target state to escalate. Yet it is not clear whether this claim applies when evidence of responsibility for the action is publicly available. We use three survey experiments to test whether denying responsibility for an action in the presence of contradictory evidence truly dampens demand for escalation among the public in the target state. We also test three causal mechanisms that might explain this: a rationalist reputation mechanism, a psychological mechanism, and an uncertainty mechanism. We do find a de-escalatory effect of noncredible denials. The effect is mediated through all three proposed causal mechanisms, but uncertainty and reputational concern have the most consistent effect.