[brational]

>My guess is, if there are two humans in the room, a "recognized leader" and a "recognized non-leader", and if the non-leader knows how to solve the riddle, and the leader does not, then the riddle will never be solved because the dog will never seek the help of the non-leader.

Why do you think that? Why not the dog search each available human for cues?

[bambax]

Because (IMHO) the dog doesn't search "humans" but "the leader", and if the leader can't help him, that's it -- it's not interested (still IMHO) in humans that it doesn't see as its master.

This should be testable and I'm surprised it apparently wasn't.