Well I don't think they know it's made out of keratin. 2 out of 3 times I go there to feed them, so why wouldn't I be made out of food? She probably thinks "Mmm this is some delicious looking brown grass".
Hard to tell with CX if they just relate you to giving food or actually like you. I do think they actually like me and I do think it's grooming, just a bit too rough sometimes. Furthermore, they sit on my lap and I can always see them eye pinning. I have the eye pinning on video but BYC doesn't allow me to upload it