Chapter 18 was a very nice touch. A more than slightly unstable Harry.
On another note, I can understand a fourteen year old not knowing the definition of a contract, but I have problems with someone of Dumblebutts stature not knowing it.
What the goblet does is not a contract by any definition of the word. Its more like a geas. A type of curse. But not in any shape form or fashion a contract, which is, by definition, an agreement.
Sorry, just venting.