I saw no type of residue in the horn and I even gave it a good sniff to see if I could detect an odor that may have been left by whatever was in it. From the looks of them the little eye hooks were either cast or forged, I say that because they are continuous, you can see a flat on the one in the base. They were threaded though, you can just barely see a thread or two at the tip. I don't think it was tobacco or snuff, too hard to get in and out. Lots of possibilities, probably never know for sure. If there were a couple of air holes I would say bait, crickets or grasshoppers.
Tim C.