Often, test participants’ running commentaries are the richest source of insight into the interactive strengths and shortcomings of a medical device, eclipsing the value of task ratings, times, and even observations. However, placing their brains on “speakerphone” can change how test participants perform tasks, potentially boosting or degrading their performance. Therefore, it is more common to direct test participants to think aloud in formative usability tests, rather than summative usability tests. However, there is no rule against having test participants think aloud during a summative usability test, particularly if the activity can help uncover use safety problems that might otherwise escape detection.