I have fooled him many many times. I chose Queen Ízlanzadi from the eragon books. He had no clue, probably does now though
If he's always getting your subject correct you're thinking too common things. While a cartoon from years ago may not be very common to you, you'd be suprised how many people would think to test it.
A few other people I can think of might be things like, The Gorl from Deltora Quest, Jenny from Rangers Apprentice. Wheras if you picked the lead and most notable characters or the title of the object itself it's very likely to come up with the answer.
Edit* Yeup, Queen Ízlanzadi is in his data banks now, but he hasn't got Wyrden, who was one of the 12 eleves assigned to protecting Eragon.. In fact out of those 12 he only has Blödhgarm

He has yet to acquire Laufin, or even Uthinarë. Then again all of the elves basically had the same appearence with the exception of Blödhgarm, and there were 6 males and 6 females, so he'd never be able to narrow down the females before he gives up as he only attempts 3 times normally.. And he'll waste at least one of the attempts on something like Arya or Eragon himself, even Vrael, the leader of the riders before the fall lol.