Depends on how skilled the person using them is. It can be just a light trace or deep cuts over non-vital areas.

[Having both given and received some quality knifeplay, Chuuya prides himself on being rather skilled with a blade.

Oh look, now the quill is writing out a nice scene of Chuuya showing off his knife skills by sliding cold steel along heated flesh.]

It just does what it wants. I wonder if it’ll keep going after we leave, or if it’ll pick on someone else that gets close.