The rat pelt is a raw material used for crafting. It rarely drops from rats. Lysis uses 3 rat pelts and a varying number of rat teeth to make a Disease Resist Amulet. Sholop uses 5 rat pelts to make a small pouch (not to be confused with the small sack).
When you give this item to Sholop he will say "A rat pelt eh... maybe with enough of these I can make something small."
Sholop and Lysis both buy rat pelts for 20 gold and sell them for 75.