Yay for mechanical coupling, which is enough of an effect to drive these into synch as long as they are all naturally oscillating close to the same frequency. This same effect is/was used in clock shops — pendulum clocks hung on a wall would similarly synchronize, giving the illusion that they must all be wonderfully precise clocks, to all be ticking at the same rate and in phase like that.

Spoiler alert: nothing dramatic happens in the last minute of the video — they just tick away. It’s tempting to try a cadence (There she was, just a-walkin’ down the street…), but the ticks are a bit fast.