Sherlock: Probably something about trying to make friends.
Mycroft: Oh yes. Friends. Of course, you go in for that sort of thing now.
I love everything that’s going on with Sherlock’s face in this scene. He is so happy and amused and concerned for his brother and also “HAHAHAHA AT LAST I HAVE DEEP AND COMPLETE KNOWLEDGE ABOUT SOMETHING YOU’RE SO CLUELESS ABOUT THAT I CAN MAKE YOU SQUIRRRRRRM.”
And Mycroft is just like, “HELP MY BROTHER IS POSSESSED SOMEONE OPEN A WINDOW SO I CAN ESCAPE.”