It may not look like much, but this simple 2014 experiment involving a helium-filled balloon and a minivan created by Destin from Smarter Every Day will make your brain ache.

It's puzzling, because the balloon in question seems to act completely counterintuitively to how you'd expect.

We're conditioned to think that when a car brakes, its contents will move forwards as a result of inertia.

But in this video, the balloon goes backwards when Destin brakes, moves forward when he speeds up, and goes against all our common sense as he turns left and right.

So what's going on? It turns out that the answer is surprisingly simple - and even though it seems to defy logic, it actually follows it.

It all comes down to the fact that helium is lighter than air. So when the car brakes, the air molecules do follow the laws of inertia and collect in the back of the minivan.

But this displaces the helium-filled balloon, and pushes it towards the front of the car, away from the collection of air molecules.

See? It all makes sense.

But don't take our word for it, watch the episode above to find out more about what's going on - it's definitely worth it.

A version of this story was first published in December 2014.