It turns out a pony could be waiting, as there appears to be the bones of some poor individual inside the rotting wood unit.
Near the front of the cask are a few long bones and the skull, but it appears to the mare that the pony died huddled near the back of the cask. Not wanting to step inside herself, she takes her spear and moves the bones around, looking for anything useful.
Unfortunately the body doesn't have anything on it. Not even tattered clothing.