• Picture an ice cube as millions of water molecules locked hand-in-hand in a perfectly organised crystal grid. It stays solid because those molecules are arranged so tightly — and holding that arrangement requires cold temperature.

When salt lands on the ice, the salt molecules wedge themselves between the water molecules. This disrupts the neat crystal arrangement and makes it much harder for water to stay frozen. 

• The freezing point drops — water that was perfectly happy being solid at 0°C suddenly needs to be colder to stay that way. So a thin layer at the contact point melts.

Here's where it gets surprising. That thin liquid layer is surrounded by a massive block of ice. The big block acts like a giant cold sponge — it pulls the energy right out of the liquid water until there's not enough energy left to stay liquid. So it refreezes. Right around the toothpick.

• The toothpick is now locked in. The ice melted to let it in, then refroze to trap it — and both things happened in the same 20 seconds.

• That's why the unsalted toothpick just slides off. No melt, no refreeze, no grip.

Curiosity spark: The same freezing point depression that makes this work is why roads get gritted in winter — and why [The Imposter] and [Sink or Float?] show similar effects with salt and density.

Find out in The Crazy Scientist Lab.