Proctorio observes test-takers for over 20 behaviors. Therefore, it flags several things. It flags suspicious head, hand, mouth, and eye movement. It flags inactivity after some time. It also flags third parties in the exam location, among other things. You can’t know when it has flagged one of your actions, but it prepares a report and sends it to the instructors. If Proctorio flags you, however, it doesn’t mean that it caught you cheating.