The serpent's mark... A mark you get that slowly changes your humanity shaped like a black snake....
*At night*
Kana is going to bed like a normal person
Kana: The serpent mark... People are getting it more and more these days..
*Goes to sleep*
*Next morning*
Kana screams in fright
Kana: The serpent mark! It's on my neck!
She checks her teeth
Kana: I'm losing humanity! I need to hide this!