Do frozen frogs sink?

Ice. Commonly found in your lemonade, not found as much as we'd hope near the Earth's poles, and found altogether too much on the inside of the hull of the Titanic. Of several surprising properties, perhaps the most obvious is that it floats.

What you need:

An ice-cube tray.
A good cold freezer.
Two glasses.
A bottle of olive oil.
No frog.

What you do:

We'll come to the frog in a moment.
Fill some of the ice-cube tray with water, some with olive oil, and stick it in the freezer. Surprisingly, along with the water freezing into ice, the olive oil will solidify too.
While that's going on pour a glass of water and another glass of olive oil. Remember which is which - you wouldn't want to drink the wrong one!
Finally, drop an ice cube in the glass of water, and an oil cube in the glass of olive oil. What happens? The ice cube should float whereas the olive oil cube sinks.

What's going on?

Ice floats on water. The oil cube does exactly what all other solids do - it sinks. That's because as its temperature fell, the oil became more and more dense, gradually hardening into a solid. The solid oil is denser than the liquid, so it sinks.

But ice does something very different. Water is a small but subtle molecule. When it cools, it starts to crystallise. The hydrogen and oxygen parts of neighbouring molecules arrange themselves to point at each other. That rigid structure causes ice to have a greater volume than water - it's less dense. That's why ice floats in its own liquid – but most other solids don't.

This also presents problems if you're an organism that sometimes freezes. The ice crystals take up more room than the water did, and if they grow too large they can burst your cells. Lettuce has this problem, which is why you don't see frozen lettuce - when it thaws; it's floppy and disgusting.

But frogs face the same challenge, too. Some species can survive as much as 60% of their body water freezing solid. They cope by using chemicals like glucose not just as antifreeze - to lower the freezing point – but also to prevent the growth of large ice crystals once they do freeze.

See here for more details, but don't go freezing frogs. It's plain rude.