Blood
This is definitely awkward... I'm going to need to break the spike, but it's a solid 10 cm in diameter. Since everything is pre-soaked, I'll only need to use spit for now.
If the wall is anything to go by, this will take a very long time.
Having successfully scratched away the surface layer of a ring around the spike I've run into another issue. I can't reach the pointy spike to create new wounds.