Three points of entry in the human skull. The ears, nasal cavity or the eye sockets. All can be fatal, but the ears are the quickest.
If you have some medical or martial arts training there is always the carotid artery.
If it is sizable and has some heft to it you can use it as a kubaton for nerve strikes and compliance holds.
Precisely. Far more lethal than a two inch knife. IMHO . There are many ways to defend oneself that people never consider using. Well said old bean.