Sometimes fishers climb up a tree after a porcupine and crowd it to the edge of a branch until it falls to the ground. Or a cornered porcupine may press its vulnerable head against a tree, exposing only its quills. Most other predators give up at this point, but a fisher has ankles that rotate 180 degrees. So it jumps onto the tree trunk, faces down and attacks the porcupine’s head from above. A fisher that finds a porcupine in the open will run in circles around it until the porcupine exhausts itself spinning around trying to expose its quills to the fisher.
Fishers are in the weasel family, BTW.