Hideous. What a slime.
http://www.ratemyhorsepro.com/harness-racing-driver-charged-electrically-shocking-horse/
From the comments:
The horse gets a jolt with the wire or electric cattle prodder while the person hits the metal feed tub simultaneously.
When they are racing the driver kicks the wheel disks on the sulky to make the same noise to scare the horse into thinking it’s going to get a shock again
That’s one of the reasons drivers get fined for not keeping their feet in the stirrups on the sulky during the race.