My left arm started to hum softly. I hated when it did that, dropping into some kind of self-diagnostic routine when its central processor figured it had the time. (The spirits alone knew what it did while I was asleep at night.) The sound was very soft, probably inaudible from two meters away, but I always reacted to it the way I would to an alarm clock going off next to my ear. I clenched my left fist strongly a couple of times, and the whirring sound shut itself off.