And by the way the person who uploaded this must really learn to edit his video first. The real meaningful part of the video didn't begin until about the halfway point.
By the way I thought the reaction was really bizarre. It's like some form of alien life form sprouting from the soil. It's bizarre and yet intriguing. The chemical being spread across is actually Mercury(II) thiocyanate (Hg(SCN)2). The chemical reactions involved in the creation of the brown "serpent" are as follow:
Igniting mercury(II) thiocyanate causes it to decompose into an insoluble brown mass that is primarily carbon nitride, C2N4. Mercury(II) sulfide and carbon disulfide are also produced.
2Hg(SCN)2 → 2HgS + CS2 + C3N4
Flammable carbon disulfide combusts to carbon(IV) oxide and sulfur(IV) oxide:
CS2 + 3O2 → CO2 + 2SO2
The heated C3N4 partially breaks down to form nitrogen gas and dicyan:
2C3N4 → 3(CN)2 + N2
Mercury(II) sulfide reacts with oxygen to form mercury vapor and sulfur dioxide. If the reaction is performed inside a container, you will be able to observe a gray mercury film coating its interior surface.
HgS + O2 → Hg + SO2
According to the Material Safety Data Sheet provided by Sigma Aldrich, the material is labeled as highly toxic, and may be fatal if ingested. It is also highly toxic to aquatic organisms, and could potential cause damage to organs through prolonged or repeated exposure.
So if you wish to replicate the above experiment, make sure you have your lab coat, goggles and face mask with you. This thing, like its namesake, can kill.