User blog comment:XGlass Reflection/Ep. 21 Review~ Holy Shit/@comment-88.153.169.230-20130907022325/@comment-2214433-20130907090228

tl;dr

The blood evaporating is Female Titan's blood, Mikasa wasn't injured at all.

Same as the Titan blood evaporating on Irvin's cheek from episode 20, Reiner in ep 17 (in contrary, Armin was covered in his own blood, thus it didn't evaporate), Hanji in ep 9. The anime has made it clear that any part of body that's detached from the Titan evaporates, that includes blood.

Anyway, let's not start insulting each other, this can be discussed peacefully.