Just as Kumokawa Maria was feeling some relief, the wall directly to her side suddenly bulged out to crush her.

[...]

“A human…!?” shouted Oumi Shuri.

It had been a human transformed to have the same texture, coloration, and luster as the wall.

[...]

“I left them all over the place so I could fight at any moment. Since their sensory organs would be wasted otherwise, I had them double as sensors for me

Toaru Majutsu no Index New Testament vol.4 main.20