I thought that while in a cave some char with high PE or big outdoorsman skill a character would hear critters (and what critters they are) in the cave
There should be some levels like:
<PE5 hear nothing or outdoorsman 100% - you hear nothing
PE 6-7 or outdoorsman 100%-150% - you can tell if the cave is inhabited (a message at the entrance)
PE - 8-10 or outdoorsman 150% + - you can tell if humanoids or animals are living in the cave (a message at the entrance)