At the beginning of Harry Potter and the Chamber of Secrets, Fred told Harry, "...house-elves have got powerful magic of their own, but they can't usually use it without their master's permission." (page28) In multiple instances, Dobby proved this to be true: appearing at the Dursley's house, stopping Harry's letters from arriving, making the pudding fly, blocking the passage to the Hogwarts Express, etc.
Dobby also visited Harry in the Hogwarts hospital wing when Harry was regrowing his arm bones after a Quidditch match. How is it that Dobby could get into Hogwarts in the first place? Isn't Hogwarts supposed to be protected by a number of spells that make it impossible for anyone (or anything) to find the school or to get in? At the beginning of this second book, Fred told Harry, "...house-elves have got powerful magic of their own, but they can't usually use it without their master's permission."
In later books, Rowling mentions that a "popping" sound occurs just before/after Dobby appears/disappears at Hogwarts. This sound is associated with apparating and disapparating. But it is said again and again that no one can apparate or disapparate inside of Hogwarts. So how does Dobby do it?
It seems that perhaps the magical powers of Dobby the house-elf are yet to be discovered. They could play a very important part in this final book as the long awaited battle between good-vs-evil takes place.
