[Nukaru]

I think it's because the little boy is the only real human in the PV.

Ayu's never moving around that much, only in the beginning and the end, so I think she's just a robot, like the one she uncovers at the end. Another reason why my thoughts are drifting in that direction: the 'underground, sparkling' Ayu, seems to controll her.
The old man seems to be a god or something (the way he's dressed, the beard, he gives a god-like impression).
The scarecrow, scarecrows are designed like humans, but they don't live.
And at least the robot guy, the way he moves he's either not very good at dancing or a robot xD Well, it's ovious he's a robot.

So I think, to make the little boy more outstanding, he actually says something (and to empathize his human-ness, he's saying it in a totally different language, so you really have no other choice but to notice him). The fact that he tries to give a scarecrow candy, is another thing, that makes him totally human, since that is a thing only a child would do, maybe he's trying to make friends with the scarecrow.

Sorry for my bad explanation, but my english isn't very well today and it's late >___<
*off to bed* =__=