Definitely not a good noise for Billie to be making. On the other hand, she's clearly off her rocker at this point, so maybe this would be mercy.

Leaving her half-dead and thoroughly stabbed isn't good enough, though. Shura needs to finish her off. Billie can come back as angry as she wants; biting it temporarily was better than living like a real rat. But Shura's just barely able to lift herself off the ground, and she has to use Fang to haul herself up on her knees. This is enough. A chill begins to fill the air as Shura draws on the scale's power. One last shot, and it had to count. That's okay, she can do this