But he quickly withdrew it in disappointment; not only was eating difficult on account of his tender left side… but he did not care at all for the milk, which was otherwise his favorite drink and surely the reason his sister had set it out for him. In fact, it was almost in revulsion that he turned away from the bowl and crawled back to the middle of the room.
Towards the end of Gregor’s first day as a bug, his sister leaves out food for him that she knows he has liked in the past. While initially excited by the offering, Gregor actually finds the first taste revolting. His change in appetite ominously indicates to the reader the extent of the metamorphosis: Even though Gregor still possesses his same thoughts and memories, Gregor’s physical form controls his actions. The transformation will eventually alter Gregor’s personality and preferences too.
Then other times he could not be bothered to worry about his family, he was filled with rage at their miserable treatment of him, and even though he could not imagine anything that might spark his appetite he still devised plans to raid the pantry and, even if he was not hungry, get the food due to him.
As Gregor has nothing to do but think in his new life, he spends time wondering about his family’s well-being and what could be happening at his old job. Here, however, he acknowledges that his anger towards his family at their treatment of him sometimes takes over, and he pictures invading their food cache and eating whatever he wishes. Before his transformation, Gregor prided himself on caring for his family and being successful in his job. Without being able to do these things, he loses his identity to the point that he sometimes resents his family instead of caring for them.