Screamy! That's how she feels. It also gets her pressing into Ellie more. 

What a lovely thing.

She's delighted that Ellie thinks so.

Of course, at this rate, Knife won't be coherent for long...

"Ready to let me say goodbye to our guest?"

Blink and dreamy smile. "Mmmm. Yes'm."

Ellie pats her cheek. "Good girl."

Giggle!

And she slides out of the body - leaving the original inhabitant with her old appearance, now very rudely awakened and screaming in shock and pain about it.

Ellie clamps a hand over her mouth. "Shh, shh. It won't hurt too much longer, I promise." She waves the knife in front of the girl's face. "See?"

Knife giggles, just out of the girl's sight.

The girl tries to sob and keep screaming.

Ellie lays the blade across her throat.

"Careful, now."

"Bad girls don't get nice things," Knife croons.

The girl is totally unable to calm herself down, to the surprise of absolutely no one, and is trying to push Ellie away. Not really succeeding at all, what with all the broken bones.

Likely she'll cut herself a bit, then- or more than a bit.

There's a tragically important number of blood vessels in the neck - the girl does in fact cut herself in her terror, and her blood sprays out as Knife laughs.

"Good night, new friend."

She dies.

"I wish I could kiss you," Knife says.

"Save it up for next time," Ellie advises.

"It's going to be a tough wait."

"I have faith in your strength of character."

"I'm not much of one for patiently holding out."

"Learning something new, then."

She sticks out her tongue.

Giggle.

"You're truly irresistible, darling."