I paused to listen too. Dogs track by smell first, then sound and then sight. Humans are different but hearing comes second with them as well. Always listen and listen carefully. Your prey makes noise escaping and those preying upon you make noise moving in for the kill (humans tend to be the loudest approaching that climactic moment; other animals, the opposite). You'd think that snaps and rustling would seem to come from everywhere. But it doesn't take long to learn to compensate for echoes, judge distances and know with more or less certainty where the source is located. After