eliminates a magic sigil

Kamijou slipped his right thumb and forefinger between those lips and forced her
mouth open.
The back of her throat.
Due to the protection of the skull, that was closer to her brain than the back of her head.
Also, people would almost never see it and no one was like to touch it. At the back of her
dark red throat was a single eerie mark like something from the horoscopes on TV. The
mark was carved in pure black.
“...”
Kamijou narrowed his eyes once, gathered his resolve, and then shoved his hand into
the girl’s mouth.
Her mouth wriggled like it was a different creature altogether as his fingers slipped
inside. The oddly warm saliva wrapped around his fingers. The unsettling feeling of her
tongue made Kamijou hesitate for an instant, but he then pressed his fingers in the rest
of the way to jab at the back of Index’s throat.
It seemed to Kamijou that Index shuddered violently with a powerful urge to vomit.
Kamijou felt a slight shock in his right index finger as if from static electricity.

- Toaru Majutsu no Index Volume 1, Chapter 4