Being Alaska, my first thought is that your "passer-by" may also be on horseback - so long as he's in a location where a somewhat prudent horseman might venture

Being Alaska, my first thought is that your "passer-by" may also be on horseback - so long as he's in a location where a somewhat prudent horseman might ventured while mounted. And maybe add similar tests for the passer-by hearing or smelling things?