"What do I do now?": Spontaneous Human Responses to Robot Effectiveness and Efficiency Malfunctions in Collaborative Robotics

Robot malfunctions are unavoidable in human–robot collaboration and oftentimes detrimental. Yet humans are rarely instructed on how to respond in such moments, leaving ample room for spontaneity and unpredictability. We studied 65 participants working alongside a collaborative robot under both normal operation and deliberate malfunction conditions. We analyzed unscripted vocal and action responses regarding situational awareness (SA)—whether malfunctions were noticed—and task-oriented response appropriateness—whether responses advanced or undermined the collaboration. During malfunctions, SA was universal, as was frustration and confusion, yet appropriateness diverged sharply: unscripted responses ranged from clarifying questions and corrective actions to sarcasm, comedic gestures, and intentional mismarkings. Efficiency malfunctions elicited far more productive responses than effectiveness malfunctions did, underscoring how actionability fundamentally shapes human intervention. Our findings reveal a fragile link between SA and task-aligned action, highlighting the need for robot transparency, explainability and adaptability, so collaborators are actively supported when things fail.