Basil looked at the scene in front of him in a slight bewilderment and fascination. He was conscious of what he was currently doing, but he didn't actually know what he was doing; he felt unfamiliar with it, but he felt so right doing it.
If he were to analogize it, it would be like having one's memories wiped clear, and then doing the habit one always did prior to losing the memory.
He had actually felt this feeling in Death Howl when he had done it to Caesar, but he felt the feeling clearer this time. No different than his first time of doing it however, he still didn't quite know what the purpose of the act.
What makes the current situation different than the one he had done back then at Death Howl Dungeon is his state: he had been half conscious when he was doing it to Caesar, whereas now he was fully conscious while doing it to Deacon.
