The sword's comment continues to unnerve you. If what you're hearing isn't just a big spider, exactly what is the source of that sound?
Sources, you correct yourself with an uneasy pause. You can tell now that there are multiple things scuttling across the bones.
You redouble your effort to determine the direction of the sounds, but it's fruitless. The bone tunnel distorts sound and you cannot tell if the skittering comes from ahead of you, behind you, or both. While you still don't see where the sounds are coming from, you do see a flickering of torchlight from around a corner ahead of you.
Closer to the bend in the tunnel, the flickering is brighter and you see long shadows dancing across the skull-covered walls. The sounds are much louder now.
You haven't quite reached the turn in the corridor.