An interesting claim to make, is sanity.
I'm reminded of Saul Kripke's Philosophical Zombie concept, whereby a person could act and interact exactly like everybody else, but have no actual consciousness, simply a staggering degree of pre-determined instructions which it follows, thus giving it the illusion of free will.
I wonder, if it acts and interacts sane, is it truly said to be sane, or is the insanity simply coming out in a different, unseen way? If you couldn't tell by being around the person that they weren't sane, does it truly mean they're sane or have they just internalised their insanity?
Not sure how well that really translated, it just was the first thing that came to mind when I saw the topic.