What are RC cells?

[Canadian]

I watched an episode lately and while watching it made me think, what are RC cells that identify ghouls as ghouls?
What is your theory on these things?

 

[Blackangel]

if anyone should have answer to it then it should be tokyo ghoul's author. no one can know what they are.

 

[Kaname]

In this story they are something that are present from the beginning.
So no one knows what they are.