>Find a decent tree to climb, then climb it.
>Look westward once we get a better vantage point.
>You find a suitable tree nearby and make your way up its branches.
>Once there, you look west again. This doesn't give you as far a vantage as you might hope, given how the land continues to rise up in that direction, still crowded with trees. If you keep moving forward, you're going to have a rather more strenuous hike on your hands soon. You still don't see anything out of place. The sound stops.
>Wait, there it is again! Just as you're about to mutter in frustration once more, you finally catch a faint hint of motion on the other side of a bush. There is a small spider creeping through the undergrowth about 25 feet away. Well, 'small'; it's funny how an encounter like you had earlier can change your perspective on such things. It's around the size of the first spider you chased and seems to be roughly similar in kind. Its coloration makes it blend in quite well with its surroundings; if it hadn't been moving, you're pretty certainly you wouldn't have spotted it at all.