One of the little details and tips the Mad Scientist wrote down in the book of Eternal Mind Zoo was that if he was the last thing a beast saw before he killed it, it would make it easier for him to drag out its Will for two different reasons.
Fear and Fury.
If he made a beast be fearful of him before killing it, the Will of the beast would be fearful toward him and would not resist when he attempted to pull it into his body.
And if the beast died with fury and vengeance, and he was the cause of it, the Will of the beast would most likely not resist getting pulled into his sea of consciousness because it would want to kill him.
Basically, the Mad Scientist advised that when killing a beast, he should ensure that the beast saw him last.
Even though he was wearing a mask, his eyes were more than enough for the Will of a beast to recognize him.
