3 ideas
Working from degraded signs rather than witnesses, Bony reconstructs what happened while the local elders, resenting his intrusion, point the bone at him. He succumbs to a wasting sickness from the curse and nearly dies before completing the case, which makes the book a concrete test of whether a trained mind can outlast a belief it rationally rejects.
Every event leaves physical residues, such as a burnt patch, a print, or disturbed soil, and each one limits which prior sequences of action are possible. The tracker's method runs causation in reverse: he asks what action must have produced this mark, then uses the rate at which wind, rain and animals erase such marks to date it. Time degrades the evidence but does not destroy it, so a cold trail becomes a problem of reading partial and weathered signs, not a dead end.
Bone-pointing has no physical agent. It works because the target knows he has been cursed and holds, somewhere below reason, a cultural belief that such a curse is fatal. That conviction produces despair, loss of appetite and bodily decline, and social isolation reinforces it. Rational disbelief gives only partial protection: Bony, raised between two cultures, understands the mechanism and still sickens, because belief laid down early operates beneath argument.