How does one know whether a person understands a device? The quality of the questions the person asks when the device breaks down.

Models of question asking predict that questions are asked when comprehenders experience cognitive disequilibrium, which is triggered by contradictions, anomalies, obstacles, salient contrasts, and uncertainty. Questions should emerge when a person studies a device (e.g., a lock) and encounters a breakdown scenario ("the key turns but the bolt doesnʹt move"). Participants read illustrated texts and breakdown scenarios, with instructions to ask questions or think aloud. Participants subsequently completed a device-comprehension test, and tests of cognitive ability and personality. Deep comprehenders did not ask more questions, but did generate a higher proportion of good questions about plausible faults that explained the breakdowns. An excellent litmus test of deep comprehension is the quality of questions asked when confronted with breakdown scenarios.