The first kill
After the teacher had made the grand announcement, all of them suddenly left and that included the one who was giving the instructions. It looked like they had vanished and the students were left standing there, stunned and confused, with no one to guide them.
"They can't be serious, can they?" Vorden said. "What should we do?"
The truth was that the teachers had actually copied an invisibility ability beforehand and were watching everything very carefully, closely.
The kids were talking amongst themselves and trying to figure out what to do. They had been playing with each other this whole time. Even if they were suddenly told to turn against each other, they couldn't just do that out of the blue.