Facial Expressions Whilst Receiving Massage

What are the acceptable facial expressions one can use whilst receivinga massage. Are you allowed to laugh when it tickles, grimace when it hurts or, slightly more embarassing, show pleasure when it feels really good? Or are you just supposed to keep a stoic look of sereness at all times. Sometimes it feels really good and one has to stifle a groan because you're paranoid that the masseur will think you're getting off on it and demand that you leave the premises. Other times, more common, they grind their elbow down into your bum or your leg bone and it's pure agony and you can barely hide a grimace or even a yelp or scream of pain and then they either keep on going sadistically or, worse, they think you can't handle the pressure at all and they completely tone down the rest of the massage and it feels like he or she's just tickling you with a feather. It can be very confusing but serenity seems like the best option ... If only they'd let me be.