Elk antler is used to hold the slate harpoon tips. Elk bone can be used instead of slate for the harpoon tips themselves:
“You can’t condition slate the same way you can condition bone where you can hang it up in the rafters, let the smoke get at it, you keep polishing it, and the little bits of carbon that go into the pores then actually act as a binding agent to give it more tensile strength.”
-secəlenəxʷ Morgan Guerin
Elk sinew is also used to tie the pieces of the harpoon together.
Videos courtesy the Museum of Anthropology - UBC