Did you ever wonder why wood “pops” when you’ve got a fire burning?
All wood contains little pockets of pitch, sap, and other flammables. As the wood heats up, the warmth penetrates deep into these pockets.
The sap/pitch liquifies, then vaporizes as the temperature increases. Gases expand rapidly when heated. As they expand, they put tremendous pressure on the walls of the pockets. Finally, the walls can’t take the pressure anymore and burst. At that time, the “popping” sound is audible.