Cyanide blocks the last electron carrier in the mitochondrial membrane from delivering its electrons to oxygen. In response, electrons get backed up all along the electron transport chain. How specifically does cyanide kill you?

In a nutshell, cyanide prevents cells from using oxygen to make energy molecules.

Explanation:Cyanide refers to any chemical containing a carbon-nitrogen (CN) bond. Many substances contain cyanide, but not all of them are deadly poisons.

Without the ability to use oxygen, mitochondria can't produce the energy carrier adenosine triphosphate (ATP). Tissues that require this form of energy, such as heart muscle cells and nerve cells, quickly expend all their energy and start to die. When a large enough number of critical cells die, you die.

this is more of a statement than a question. is there answers to go along with this, or is it opinion based?

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.