@Sapphire haha. Yay!
Nikki: Nope. ^.^
Actually this one's less a stumper and more a "there's absolutely no way you'd get it" joke.
It's a herring. But a herring isn't on a wall? Surely you could mount it and hang it. But they're not green? Well, paint it. Not wet? Of course it is, you just painted it? Oh, the whistling? ...Well, couldn't make it too easy, now could I? ^.^;;
I need to come up with one that will truly stump him, now...though Nikki may not care about being fair.
Nikki: *asks him a riddle she doesn't know the answer to*
later
Nikki: Well I asked you because I didn't know~!