The light left on: all three arrows turn together, the same way, all the time.
Tricks of motion
Stroboscopic effect
The arrow on the left turns steadily. What about the others?
They turn the same way, but are lit only by flashes, so they seem to stand still or turn backward.
Why? You only see the arrow during the flashes. If it has turned exactly once between flashes, it looks like it hasn’t moved. Mechanics use a strobe light like this to check fast machines.
Picture: Drawn by Science Playground · Wikipedia(opens in a new tab)