Herbert does his best to brace but his forepaws aren't exactly as large and versatile as his human hands and he's lying on Ignatius so he has to entirely stop cutting and essentially try to use his wrists in the wound to stay on.

"Make yourself useful, Strange!" he shouts, digging his back claws into the robe rucked up around the fae's upper torso. "Calm down your fae!" He isn't aware of whether or not fae even have an immune system that would deal with expelling iron from the wound. This may be Ignatius' only chance to deal with it, lest it seal up around the infection.

Herbert honestly really wishes he had a book on fae anatomy. Nothing here really makes sense.