In regard to this theme Magritte said that he was trying to put himself in the place of prehistoric man when he first discovered that fire resulted from striking two stones together. He shows fire leaping up out of a piece of paper, a key, and an egg; and, as in other paintings, the large, upward sloping surface with grained wood plays an important part. An earlier painting of the same theme (formerly in the Mesens collection), in which the fire leaps up out of paper, a chair, and a tuba, was painted in 1933.

Magritte reminds us here of fire as an absolute phenomenon, which can originate from stones without devouring them. The egg, the key, the paper, the wood, the tuba, the sofa, used in relation to the flames of fire, seem for a moment as absurd as the stones which also give birth to fire. Magritte was fond of thinking in categories: light, air, fire, earth, rain, sun, window, sea, tree.