For those interested, longleaf pine has a long history of being taped for turpentine along the southeastern coastal plain. There are still some old "catface" trees on the landscape that carry the scars from long ago.
Later, after many of those old trees were hi graded, the stumps were dynamited out of the ground and turpentine rendered from them. So, if you're ever in the pine flatwoods of south Alabama, Georgia, or north Florida and come across a big hole in the ground, that's probably what happened.
So, fatwood (or lighter knot) is basically wood soaked in turpentine.