Ah, it was a disillusionment charm on the Hippogriff. Pretty Awesome. Nigel did not understand why expect for the obvious against the law for muggles to see them. Other than that. Nope not one thing popped into his head. Though it would be a pretty hard challenge to have to take care of a disillusioned hippogrff. Especially if it does not like you.

"For the challenge"

The Seventh Year answer might not make any sense. but who said he had to make any sense. Riding a disillusioned hippogrff sounded awesomely awesome, though.