7) How Did Sherlock Not Notice The Missing Glass?
Once they arrive in Sherrinford, Sherlock has a chat with his little sis where she keeps teasing him for missing the obvious. Eventually, he puts his hand to the glass of her cell… only to realize that there’s none there. She only made it look like there is by using a few suspended signs and a microphone that feeds her voice through the speakers.
This is undoubtedly a clever rug-pull for us as the audience and a nice way of revealing that Eurus is really in charge of the facility and can leave whenever she pleases. However, it makes no sense whatsoever that Sherlock wouldn’t have noticed that there was no pane of glass only a few feet away from him. Obviously, he’s undergoing a very traumatic experience at the time – he’s meeting a sister he never knew he had for the first time – but his deductive capabilities can’t have deserted him so completely.