A rationalist can accept the emotional and social force of a supernatural legend while refusing its supernatural premise, treating the fear itself as a real cause that a human agent can exploit. The hound's terror operated whether or not the hound was magical, so the belief functioned as a weapon independent of its truth.
A murderer coated a large living dog in phosphorus to make it glow and appear hellish, then used it to frighten an heir with a known heart condition to death, exploiting the family's existing legend of a demonic hound. The method worked because the victims already believed the curse, so a mundane dog dressed as a myth became an untraceable instrument.
An investigator can plant himself hidden near a scene and gather evidence while a visible proxy is believed to be the one in charge, so suspects act freely under the assumption that the real analyst is absent. Concealing your presence, not just your conclusions, lets you observe behavior that would change if the subject knew you were watching.
Physical traces left in a landscape, footprints, the direction a walking stick was gnawed, mud specific to one locale, can reconstruct events and people more reliably than testimony, because the environment records what witnesses omit or distort. Reading place as evidence treats terrain and objects as a factual record rather than mere backdrop.