For example, when Peter sees the letter of the Tulip, if you look at his reaction your not sure what kind of reaction that is. Does he remember something that he shouldn't because of his experience in shifting out? Is it just a realization that Walter probably doing something significant.
Here is the other moment. When Michael presses his finger to his lips to Olivia and gives her the "shhh" gesture you are not sure what this means. When Olivia uses her abilities at the end...he makes the same gesture again. Almost none of the Reviewers of the episode picked up on the significance of those two moments. It means in my opinion that Walter was wrong. Injecting her didn't result in temporary return of her powers. She has them beck period. That's why she could summon up her powers at the end. It's why on her final shift or at the end she didn't have a withdraw episode.