Black snake and Pharaoh's serpent are two similar types of outdoor firework.
After lighting the small tablet, both fireworks start smoking and an ash resembling a snake is created via 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 creating black snake. Other sources report the contents as "a nitrated mixture of linseed oil and naphthalenes".[1]
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.[2]