In this scene, Christopher is going into the London tube. When he arrives he has a sensory overload because there were too many people too close to him and he didn't know how to get on the train. Christopher's coping mechanism is going into a photo booth, which is a secluded and quiet space where he can relax.
When on the escalator, Christopher experiences a sensory overload because he has never been on a staircase that moves. He starts to have a panic attack and gets really anxious because the escalator is so crowded and he wants to get off of it.
After not knowing what to do to get on the subway, Christopher feels anxious. When more and more people board the station, Christopher has another sensory overload because of the amount of people, blaring signs and sounds, and the feeling of being trapped in a tunnel with no windows or room to move.
When he feels uncomfortable, Christopher sits at a bench. However, when he is looking up at the big crowd in front of him, he begins to groan and feel sick because he can't think straight when there are too many people and sounds in one small place.
Christopher's sensory overload causes him to feel sick, and he wonders if he should go back to live with his dad and not continue his journey to his mother because he is in a new place. that doesn't make him feel good.
Christopher has a sensory overload because when the train pulls in it sounds like wind and the people talking sound like sword fighting. All of these sounds together cause him to not think clearly and want to be by himself. All of these factors that cause his sensory overloads make it harder for Christopher to take the train to see his mother because it is hard for Christopher to adjust to his surroundings.