Is anyone else the parent of a painfully slow eater?

My son (4) never used to eat so slow, but for the past week or so he will seriously take an hour to finish even the smallest meal. For example this morning he had half a bagel for breakfast and he sat at the table and took over an hour to finish it all. And at supper he will take just as long to eat a child-sized portion. How do you maintain your sanity with a super slow eater?