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The recruits performed relatively well after the purpose of the lesson became clear. Some lucky ones managed to use their mana correctly right away, which led to quick kills, but most ended up in long battles that forced them to overcome their anxiety and disgust.
Khan didn't let the robots clean the hangar, so the floor grew dirtier after each battle. A few recruits had to attack while their opponents fed off the remains of the dead Tainted animals, which naturally affected their ability to focus.
The lesson succeeded in making the students experience part of the battlefield, and even those who didn't fight gained something out of it. Defeating those Tainted animals was far too easy for them, but the actual killing was hard, especially when they had already won, and that was enough to accomplish what Khan had in mind.