The face-slap...
Outside the SSA, General's Residence Building, Meeting hall.
"There are only three ways to kill a hydra properly, if not killed properly it would regenerate to full health if given enough time, thus making your mission a failure…" (General)
"Thus if the students want to finish this mission successfully, they have to at least do one of the following things to kill that hydra…." (General)
The first method to kill a hydra is by cutting or destroying it's all its five heads together, which is a very difficult task, a single person may find it impossible but since there are many students to fight it, this method may seem actually the most feasible but this is the most dangerous one.