What is December's mystery sound?
Your clues are: The oldest one of these is 45 years old. The largest one is 10.5 metres circumference. You could have a fight with these on Mars. If you sped me up, you’d have to duck twice as fast.
What do you think the answer is?
We challenged our experts to guess what is making this strange sound. Can you guess what it is?
The answer is: a snowball in slow motion!