Well, I see at least one twitch in that GIF, although it's not on the face. Check Dr. Manhattan's neck near the last frames. Such a twitch might be associated with feelings related to morbidity, particularly when one is trying to hide them.
On the other hand, you might be missing out on a beauty of the artistic expression of the clip, which only applies the first time you watch it: No matter where you choose to focus on the face, you don't notice any facial twitches.
If there were a single twitch then, odds are, many people would notice it, simply because every viewer might focus on a different part of the image. This would spoil the fantasy that one must be well trained to see them, and the poetry of Ozymandias' statement. Wouldn't it?
For that reason, I'm fairly certain that the actor in this clip was trying to suppress all twitches, in order to more appropriately convey the idea that they are hard to notice. Could you really definitively say that there are no twitches, without re-watching the clip several times, checking all points of the face?
Doesn't re-watching something always destroy a bit of the magic? It's a shame, really. ;-)