I'm really interested by their body language in the pictures. In season 1, there's a lot of space between Benedict and Martin, and Martin has his arms crossed, signifying slight discomfort (though he could just be cold). Season 2, they're closer and have more open body language, showing they're more comfortable with each other. Season 3, they're in each other's intimate space (very close - touching), showing they're very close and comfortable with each other. I love it!
This made me think of my friend Emily (who is Sherlock) and I at camp this past summer. She was stressed out so she just wanted to be a burrito. So I went and got my sleeping bag and we both wrapped up in them and mayest on the floor for awhile like that. Then I got up and she stayed like that for awhile.