Have you ever used a perfume that had the wood and leather like smell to it? Something that felt coming from right out of the woods? If you did, then it was probably castoreum. This particular secretion comes right from the castor sacs of beavers and the sac happens to be located inside the anal sacs. Yes, we are using a material that has to be derived from the butts of beavers. The animals use it to mark their own territory but we use it to smell good. Quite weird indeed!