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Some of you may remember an indoor firework trick called the ‘Pharaoh’s Serpent’. The party trick displays the wonder of chemistry and has been around since Victorian times. When a small pellet of mercury thiocyanate - a compound that contains mercury, sulphur, carbon and nitrogen - is ignited, it decomposes in its own heat and the carbon and nitrogen combine to make a complex network. Other gases released get trapped inside, causing the emerging polymer to swell. The reaction keeps going until the fully formed snake reaches 100 times its original volume.

Chemist Tom Miller, from University College London, UK, demonstrates how it works.

(Image: Pharaoh's Serpent, Credit: Andrea Sella.)