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.

Getting deeply stabbed multiple times in the gut can severely mess you up, causing all kinds of nasty body fluids going where they shouldn't. Yikes.

There were also the stabs to her back which could possibly reach her lungs or her heart, and the final knife attack has him extending a lot of effort to not only stab, but carve a path through her torso. That attack was actually one of the more viscious ones in the series.