A while back, Quackity had found Wilbur over a dead body he had been drinking the blood from. He had tried to kill Wilbur with a silver cross, yet Wilbur had managed to find his way to get Quackity to not, so Quackity took him in, just didn't allow him out whenever he got hungry, plus made sure he wore eye contacts out if he did.

Wilbur was hungry and knew Quackity would scold him if he went and killed another person, so he went over to Quackity, pinning him down and biting his neck.