For this effect, we provided two highly realistic heads cast in fire-retardant gypsum plaster. A hollow body was outfitted with gas lines and an ignition rig, and matched with the actor's final position in camera. The flames enveloping the body double were later composited with footage of the body coated with ash to get the final effect. A humorous touch was added in post production, when the eyes blinked open in the ashy body and hung in the air as the body crumbled away, then dropped down into the pile of ash.