Ever wonder what happens when you set fire to a jar full of gas?
The real question is… what gas?
The blue flame suggests complete combustion with no soot, even in a closed environment like a jar, so it has to be a small molecule. Also, the way the flame front travels down the bottle like that (and the fact that it stays in the bottle quite well to begin with) implies it’s heavier than air. Combustion doesn’t appear too vigorous.
I’m going to hazard a guess at either a small alkane like ethane, or possibly methanol vapour.