Vampyr, on 2013-March-04, 15:14, said:
None of this is what involuntary means. You could avoid making facial expressions if you wanted. You can also choose to make them at will.
Then you and I have different understandings of "involuntary". If you step on a tack and say "ouch", I think that's involuntary. Yes, you could avoid it if you wanted (you'd probably have to know ahead of time that you're about to step on the tack), and you can also say "ouch" when you haven't actually been hurt. But these other voluntary, related actions don't make the original one voluntary.
It's like breathing. You can hold your breath (for a short while), and you can also "take a breath" when the doctor tells you. But ordinary breathing is involuntary, much like automatic facial reactions.
There was a show on US TV a couple of years ago called "Lie to Me", about a researcher (based on an actual person) who had studied lying and other emotions, and discovered a number of subtle, involuntary clues in body language that almost always accompany them. People also recognize many of these clues subconsciously. If you have a "hunch" that someone is lying, it's likely that something like this is involved.