What is the "Hey Fox wake word" clip in Settings?

A short recording of you reading a passage full of "hey"- and "fox"-like sounds. It tunes the on-device wake word to your voice so it fires when you mean it and not mid-sentence. Record it in Settings → "Hey Fox wake word" ("Record now" → "Stop & save"); "Re-record" or "Delete" it there any time. The setup wizard asks for it too ("Teach “Hey Fox” your voice": press "Calibrate Hey Fox", allow the microphone, read the passage that appears, then "Done"). The wake word itself runs on your device; no audio leaves it for that.