Melissa is consciously aware that someone is following her.
She did not even need to look back to confirm who it is and could only guess that Matthew is following her. Because the moment she felt that something is not right, she suspiciously suspect that Matthew is the one stalking her. And she's right about that. Because Matthew was trailing her, following wherever she goes.
Matthew could feel her discomfort. He surmise that Melissa already knew that he is just in the corner, secretly following and observing her from a distance. Yet, why wouldn't she even stop and confront him? Its as if what he did is completely bearable!
Matthew felt annoyed by her action, Melissa purposely avoided him. But knowing him? He wont allow himself to be left unnoticed. Determined to get her attention, he chase her.
In spite of doing her very best to escape from his trap, she couldn't avoid him. Matthew quickly chase her and easily grabs her arms forcefully.