The black chick at the beginning…

I guess the killer knew where the organs were located and how to place the knife. It's probably not worse than the first kill in the first movie. There's not much of a chance you could gut somebody like they did to Steve with just one slash.

Even though Steve is only heard to be stabbed and sliced once, his torso is immediately mutilated and hallowed right after the first stab.
° Unless it was a huge knife or another type of bladed weapon, this seems highly impossible unless they had "prepared in advance".

How are you so sure; not being a doctor?

We’re told she was stabbed 7 times, and it wasn’t just to the stomach, it was through the back.

7 massive stab wounds in the mid-section would easily kill someone. She actually lasted quite long, considering.