Doing any serious analysis on the "zombie look" is probably not possible as we dont have any certified zombies to compare against.. But my (serious) thought are these:
1.) There are people who do not look like "zombies" to me, but who nonetheless manage to what I regard as "precision playing" - The only issue in Coalports last posting which I completely disagree with is with reference to Clara "Even the muscles of her face were relaxed (hence the blank, faraway, "zombie" expression)" - I do not think Clara ever shows anything remotely looking like a >> "zombie" expression <<
2.) I think there are some people who are more "natural" with the theremin than others - Precision thereminists, in my view, have varying degrees of this "natural" ability, and that this largely determines the extent to which they carry the "zombie" look -
3.) I think there are people who, through massive effort and dedication can master precision theremin playing despite having a lower level of inate "natural" ability than others - It is these people who most exhibit the "zombie" expression - They are not able to relax or spare any thought or allow any distraction of paying attention to how they look - they require everything they have to be totally focussed on the one thing - playing.
4.) Often, in my view, the focus on precision by those who are not "naturals" impacts on their performance in other ways than just their "look" - Despite the improvement (or because of it) in the precision of their playing, their performance carries less "life" or "emotion".
5.) I think that there is strong pressure for some who are or aspire to be "pro" thereminists to concentrate more on "precision" than on the "emotional" aspects of their performance - If they are off key or make any other technical errors, they will be jumped on by other precision thereminists and their flaws ruthlessly exposed - This "feedback" is mostly intended to be constructive - However, If someone produces a technically perfect performance lacking in "emotion" they will not recieve any (or anything like the same degree of) "constructive" critisism.
This was brought home to me some years back, when an extremely hard working dedicated thereminist (who IMO looks more like a "zombie" when playing than anyone else I have seen, LOL) produced a relaxed and IMO highly entertaining video where he was not concentrating on precision, and didnt look like a zombie. I have looked at this individuals "precision" performances, but none of them ever touched my musical "soul" .. The only piece this thereminist has ever produced which I really enjoyed was this one relaxed performance.
Alas, this one performance fell well short of what was expected even from an aspiring "pro" - There were loads of pitch and timing errors and other "horrors" - And the "constructive critisism" machine kicked in at full force - But entirely ignored the life and fun and "emotion" of the performance.
There are, IMO, few people who have the ability to play precision theremin AND impart "spirit" and "emotion" to their performance - and these people tend to look less "zombified" than others.
Given the choice between "precision" and "soul-lessness" I personally prefer to sacrifice precision. I think that there are thereminists who look like zombies because they are trying too hard to be precise and are performing in fear of what the critics will say. The fact that they look like zombies doesnt bother me - but the fact that is that their music doesnt touch me.