Why is Harrison still in the hospital?

Okay, so, totally innocently I asked the doctor today when Harrison can start eating the coolest food ever, garlic mashed potatoes, and that's when he told us that it may be a good idea for him to stay in the hospital for a few days longer.  He sort of looked at me like he was contemplating whether or not I was kidding, and I didn't flinch one bit.  Well, he told us we should just settle in for about another week as Harrison learns to eat milk.  Potatoes come much later, you see.