After lighting the small tablet, the firework starts 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.
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.