Kangaroo whistle

I don't know if kangaroo repeller whistles actually exist, but deer repeller whistles do. The theory is that the ultrasonic tone from the whistle, which is mounted in front of the car, usually on the bumper, warns nearby deer to avoid a collision. Whether they work is debatable.

The other theme in the cartoon is the fantasy that reversing something simple, e.g. direction, polarity of battery, etc., can cause the reverse of a complex effect. I was reminded of this watching a Shaun the Sheep episode where Bitzer acquires a magical whistle that makes him master of the animals. Unfortunately he drops the whistle and reinserts the battery the wrong way around. The result was that actions got reversed. The farmer fixes the mess by grabbing the whistle and making Bitzer un-receive his whistle, restoring order to the world.

Anyway I'm also allowed to fantasise that one exists for humans. But repeller or attractor, or dual purpose? Ah, I'll leave that one ambiguous.