Anyone else notice that Mary doesn’t move an inch when John kicks Sherlock’s chair? Mrs Hudson is so shocked that she jumps up and Sherlock kind of moves like he wants to go towards John and the way he opens his mouth is almost like he wants to say something to calm John down but he changes his mind. Mary is the only person in the room who is seemingly not bothered by Johns anger. I’m sorry but if you claimed to care for and love someone as much as Mary did throughout ‘His Last Vow’ then you would at least flinch or change your expression somehow if they acted like this. John is clearly very distressed and Mary doesn’t care at all.
1. Just because you love someone, doesn’t mean you’ll automatically flinch or change your facial expression when the other person is angry.
2. It could just be how she is as a person. I personally am not the jumpy type of person and my siblings and I were known for our lack of facial expressions which resulted from a very tough upbringing. Not all people flinch or change facial expressions all the time.
3. You’re assuming a lot from very superficial reactions. People do have more dimensionality than the expressions they feel.
She’s also an ex CIA assassin who has probably been through more violent and unpredictable situations than the average person. She is trained and conditioned to be calm in upheaval. Mrs. Hudson most likely had a years long relationship with a man of questionable morals (very possibly abusive). Therefore, she reacts in fear and panic because that is what she knows to do.
Going a little more in depth, one of the things you tend to learn as an actor is that the person in control moves less in a scene than the person who is out of control. Who moves here? John and Mrs. Hudson. Mrs. H is blindsided by what is going on and startled by John’s violence. John is angry, emotional, falling apart, and becoming hysterical and violent, with good reason. Sherlock almost moves, but changes his mind. He’s physically compromised and knows he will be useless trying to subdue John if it comes to trying to hold him back. He’s letting John react because Sherlock needs to maintain the upper hand. He’s holding the situation together.
Mary has the most control here. She is also the most vulnerable, so she absolutely needs to keep it under control. She knew this would be John’s reaction and anything she tries to do to diffuse his anger will only backfire and everything will fall apart before they can address things. With her background, she would know how to navigate unstable situations with complete stoicism. She’s already had the power of revealing her secret to her husband taken away from her and this is her last bit of power left. Mary knows John and knows that comfort is not the way to go in that explosive moment. Her reaction to him drives everything, and she is handing him the freedom to react how he needs to, to do as he says, and to hand over her secrets. She has the ultimate control in doing so. This isn’t Mary not caring. This is Mary caring so much that she is choosing to stay, to do things John’s way, and to let him rail at her rather than walk out, demand he calm down, or yell back. John is on a single track of fury that is unhinged. Mary dictates the outcome, the direction of that fury; she has to be in control - stable and fixed.