I wonder if the alarm rings because we truly detect it's CG or if it's just that the facial features would be weird no matter what. I mean, in real life that face would be very weird. Maybe what we're feeling it's just that, not the detection of CG per se... Or maybe both?
EDIT: sometimes certain people have faces that look kind of CG to me, but I know they are real.
For instance, this woman has always looked CG to me in The Expanse:
I know she's real, but I dunno... maybe she has a very symmetric face and the unnatural lighting does the rest.
What if... we're all CGI?