A combustion fluid: fuel ignites only where it is hot, releasing heat, soot and volume that the pressure solve turns into bulging, vorticity-curled tongues of flame over a burning floor. Drag to spray a flamethrower jet, click to set off a fuel-air blast that shoves the air outward and flashes into a rolling fireball — MacCormack-advected for crisp tongues, coloured by Planck blackbody radiation, and shaded with bloom, heat haze and fire-lit smoke.