Reeds bend in a storm, trees break- and ice cracks.

Someone (Moriarty?) has taken Mycroft prisoner. Their shameless mistreatment of him eventually causes Mycroft to break- he's unable to hide how uncomfortable he is, possibly even trying futilely to turn away or get them off him despite knowing it won't work. They mock him for reacting and rub it in his face.

+ if next time Mycroft sees Sherlock afterwards, Sherlock can tell he's shaken and is frightened by that.