An interesting thing to note is that the Ring of Charos is shown only to work on weaker-minded creatures. The fact that it works on the Fossegrimen can be taken to show that she is a simpler being than she appears to be, also you can contact her while sitting down, and her face will be much more transparent. While wearing or having Fremennik sea boots in your inventory and giving the gift for her, you will get two more charges - four for a shark/a bass, five for a manta and six for a turtle.