Rob had lost a fair amount of his ability to feel emotion, and he was having trouble explaining it to the few humans who remained in his life. He tried comparing it to being chased by bears (and not feeling any alarm or urgency, but knowing that you should) but none of them had ever been chased by so much as a single bear.
Food, though, provided a reasonably apt comparison: Rob had spent most of his life enjoying many kinds of food, and appreciating the experience of different flavors and textures, and this had always been one of his motivations for eating food. Now, the enjoyment was gone, and only the memory remained, saying, You should really be enjoying this. What happened to you?
And in the analogy, he kept eating anyway, even though he didn't particularly care for it. For one, he had to eat something. But it wasn't just that; he continued to eat things that he supposed he would have enjoyed, had he not been somehow broken, and ate them in the hope that it would eventually return to him, that he would appreciate the food once again and all would be well. That was what he did, now: continued on as though nothing had changed, and he waited for it to change back.
And here, in the interest of laziness, is a page from one of my school notebooks in seventh grade, and the first known appearance of milk beetles: