Traveling through the fog, the only sound that Toz and the cats had heard were Toz's footsteps as he stepped on fallen branches and the rustling of leaves as he passed through the vegetation.
Not even the sounds of birds and insects existed in the silent world of isolation that was the fog. And every little sound that Toz and the cats made quickly died in the dense mist surrounding them.
So when Scrael carefully asked the others to be quiet because she heard something, they obliged. Any sound, no matter how quiet it might appear in the fog, would be far from quiet outside the fog. It also meant that the group was very close to something that might or might not be related to the source of the fog.
Being close to the next step in the mystery had the group carefully and silently follow Scrael as she led them through the fog, using her better hearing as a spirit beast at the fifth level.