Here's the secret — you didn't poke a hole. You moved the bag out of the way.

Zip-lock bags are made of a plastic called polyethylene, and polyethylene is made up of millions of tiny chain-like molecules called polymers. Think of them like a pile of cooked spaghetti. Push a skewer through slowly, and the strands just shuffle aside and wrap around it — nice and snug. No gap. No drip.

Scientists call this elastic deformation — a fancy way of saying the molecules stretch without breaking. The bag literally hugs the skewer tight enough to keep every drop inside. The same elastic behaviour is what keeps the rubber balloon intact in [The Water Balloon Timebomb] — polymer chains stretching rather than snapping, even under heat.

Pull the skewer out, though... and those chains spring back. That's when the water escapes. The bag was never broken — it was just holding its breath.

You'll find the same long-chain polymer molecules doing something completely different in [Instant Snow] — there they absorb hundreds of times their own weight in water instead of repelling it.

The same principle appears in self-sealing tyres and even some spacecraft fuel tanks. You just did that with a bag from your kitchen.

Want to know why pushing it in slowly is the key — and whether you can do it with three skewers at once?

 Find out in The Crazy Scientist Lab!