The phrase “tooth and nail” means exactly what cute little Mary Ann means when she goes after her pestiferous older small brother who is torturing her dolly.
She bites and digs in with her nails. And she and her ancestors before her, both sides of the family, have been using those natural weapons of offense and defense since Noah was a pup.
Thus with tooth and nail long ago became an English phrase signifying “with all the powers at one’s command.”
The old Latin equivalent was toto corpore atque omnibus ungulis, “with all the body and every nail.”
In France, it’s bec et ongles, closely approaching our English phrase, but with the literal meaning, “beak and talons.”