Try a rasp, sharp knife,or chisel to remove the hard tp surface, and then use needle point pliers to pull out the thread like filaments from the bottom this worked for me. I gave up on the Horse Hoof but a member from dpown the South kindly sent me a pile of Crampball which I dont think we get up in Scotland and it works really great In fact you can hardly put it out once lit.
Hope this suggestion is of help