The externally transition that Gregor undergoes is very sudden and abrupt. He awakes to discover that he been transformed into an insect. He even still sounds human enough that he assures his mother that he is getting up out of bed soon. The voice soon dissolves into unintelligible animal squeaks. He begins to worry about his career, his duties, and his relatives.
Although the external changes were sudden, the internal changes only come gradually. As time passes, his behavior becomes more like that of an insect. He is often frightened by sounds and turmoil. He seems to be more relaxed in dim, murky places. Whenever he becomes startled, he automatically darts in various paths. Although Gregor is distant from entirely being an animal; he would not bear if he didn't maintain an individual logic of responsibility, aggravation, fondness, reminiscence, and frustration.
When Gregor's voice through the door is no longer understandable, his mother finally becomes worried and instantly sends for the doctor.
Gregor observes that people now believe that something is wrong with him, and are ready to help him. He does not seem to notice the opposite side of this, which was that before it was clear that anything was seriously wrong, his family seemed to be concerned only that he was late to work. When Gregor emerges from his room to show the others what has happened to him, his father at first clenches his fists and appears hostile, then breaks down and weeps. It is not at all clear that the father is actually concerned for his son. Instead he seems to be concerned for their livelihood, and when Gregor emerges in a form clearly unfit for work, his father at first seems simply to be angry with him as if Gregor were playing hooky.