It tanks her IQ

The black tendril planted on her brow thickens and contracts rhythmically, rippling from the tip towards the depths of the book’s pages, and with the pulsing thrums a powerful *squelch*.

Hermione gasps, feeling lightheaded as her brain lurches forwards in her skull, vibrating while the tendril’s magic gradually starts to iron out wrinkles. The young gryffindor’s eyes cross and her trembling lips fall open in a perfect little ahegao expression, completely betraying her regular personality.

“Ahh-hnnghoooaa-!” Hermione groans and arches her back as the book continues to suck and pull on her scalp, draining her IQ by force. Each time it pulsates, another IQ point is rubbed out of her vulnerable young brain and slurped up by the eldritch entity, permanently erasing a class, a memory, or even a name from the poor student’s mind.

“Nnnnghiiiioaahhh-!!!” She wails and kicks violently, writhing in ecstasy and panic as she feels her intellect slipping away. Just moments ago she was resting pretty at an impressive 145 IQ, but only a few shuddering gulps later she is already down to 120, dangerously approaching the dreaded “normal”. Hermione’s greatest strengths, her magical prowess and her mental acumen, are being stripped from her.