A snake to hang over a heat source and will twirl round.
A4 card, scissors, thread, a heat source (radiator will do), colouring pens, sellotape
Colour in one of the snake templates. Then carefully cut the snake out so it looks like a spiral. Then cut some thread off. A foot should be enough. Then attach to tail of snake in the middle with small bit of tape. Then hold up the spiral snake over the radiator and it should slowly spin round like a snake on a tree. You can explain about heat rising.