Take a look at my "squirmy" script, which should still be around. This randomizes all movable parts within certain limits, and at random times, resulting in anything from a natural-looking occasional twitch to a grand-mal convulsion, depending on settings. It doesn't act on all facial parameters, but could easily be modified to do that. Look up "squirm" in this forum and you should find the thread containing this script; a few weeks back, if I recall right.

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