Why did Bo-bo put his fingers to his mouth?

The manuscript goes on to say, that the art of roasting, or rather broiling (which I take to be the elder brother) was accidentally discovered in the manner following. The swine-herd, Ho-ti, having gone out into the woods one morning, as his manner was, to collect mast for his hogs, left his cottage in the care of his eldest son Bo-bo, a great lubberly boy, who being fond of playing with fire, as younkers of his age commonly are, let some sparks escape into a bundle of straw, which kindling quickly, spread the conflagration over every part of their poor mansion, till it was reduced to ashes. Together with the cottage (a sorry antediluvian make-shift of a building, you may think it), what was of much more importance, a fine litter of new-farrowed pigs, no less than nine in number, perished.

While he was thinking what he should say to his father, and wringing his hands over the smoking remnants of one of those untimely sufferers, an odour assailed his nostrils, unlike any scent which he had before experienced. He next stooped down to feel the pig, if there were any signs of life in it. He burnt his fingers, and to cool them he applied them in his booby fashion to his mouth. Some of the crums of the scorched skin had come away with his fingers, and for the first time in his life (in the world's life indeed, for before him no man had known it) he tasted—crackling!