Confirm a real, live person is at the keyboard: presence detection plus a random sequence of on-camera actions that a replayed or generated video won't produce on cue.
This is a client-side preview so you can experience each check. Inside a real Carrier experiment, challenges are generated server-side, answers are verified server-side and never appear in any client payload, and every result is recorded on the participant's run and interleaved into the session transcript.