The traditional "Pharaoh's serpent" version of this firework produced a more impressive snake, but its operation depended upon mercury thiocyanate, which is no longer used because of its toxicity.
Video of mercury thiocyanate.
(Bad wikipedia link BTW)
The traditional "Pharaoh's serpent" version of this firework produced a more impressive snake, but its operation depended upon mercury thiocyanate, which is no longer used because of its toxicity.