Thinking about the freak-out abilities of all of these body parts that I am creating, it strikes me that there is a deep-rooted psychology in things having to do with the face.
As humans, we tend to anthropomorphize things into human facial features, seeing faces where there aren't any. Two circles and a line become a smiley face, capable of expressing emotion. :)
I don't know where this comes from. I would suspect that it is hard-wired into our neurons so that as babies, we identify with "mother" and "father" more easily.
It is so hard-wired in that seeing a face that is missing parts, or seeing the missing parts just by themselves triggers in us a dissociative reflex. Seeing just an eyeball, or a nose, or a cut-off ear in isolation triggers this identification-- we want to see a face there, but there isn't one-- and it breaks those connections in a disturbing way.
This is more prevalent with eyes than anything else. We deal with eyes every day. It is the most recognizable feature in the face, and the part that we focus on when we are talking to someone. As such, we are hyper-aware of the reality and complexity of the eye, which makes it inordinately difficult to model well. You have to be nearly perfect to make a believable eye.
Ears are a little more forgiving. We all know what ears look like, at least in a general sense. And there is so much variation that some changes in the shape and color are expected. We don't focus on ears.
Take this to the concept of internal organs. The vast majority of us don't really know what our organs look like other than some drawings in an anatomy textbook. There is a whole lot of leeway there, but there is also less impact: which is grosser, a liver on a table, or a set of eyeballs?
Context helps. Seeing a heart taken out of a chest cavity has much more impact than seeing one just sitting in an autopsy tray. Likewise, seeing an eye being pulled out of an eye socket is deeply disturbing, particularly if the patient is conscious at the time.