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Black snake and Pharaoh's serpent are two similar types of firework.
After being lit, both fireworks begin to smoke and spew out ash resembling a snake via an intumescent reaction. They stay on the ground and do not emit sparks, flares, any form of projectiles, or any sound, but may release smoke.
Sodium bicarbonate which produces carbon dioxide gas, and sugar forming carbon containing ash, are common chemicals used for the black snake demonstration. Other sources report the contents as "a nitrated mixture of linseed oil and naphthalenes".
The traditional "Pharaoh's serpent" version of this firework produces a more impressive snake, but its operation depends upon mercury (II) thiocyanate, which is no longer commonly used because of its toxicity.