Jack has recently realized that he is the only person in the family who needs help to eat. Well, he's had enough of that. He insists on feeding himself now.
In fact, it is almost to the point that he refuses to eat yogurt unless he feeds it to himself. (As an aside, the kid is demonstrating a disturbingly high level of stubbornness. I'd like to say that he gets that from his mother, but...)
This is one of the first times that Jack fed himself.