As Aunt Marge started to make herself at home, Harry caught himself thinking almost longingly of life at number four without her. Uncle Vernon and Aunt Petunia usually encouraged Harry to stay out of their way, which Harry was only too happy to do. Aunt Marge, on the other hand, wanted Harry under her eye at all times, so that she could boom out suggestions for his improvement. She delighted in comparing Harry with Dudley, and took huge pleasure in buying Dudley expensive while glaring at Harry, as though daring him to ask why he hadn't got any a present too. She also kept throwing out dark hints about what made Harry such an unsatisfactory person.
Harry Potter and the Prisoner of Azkaban
What does "dark hints" mean here?