In Czech it is "Běž! (Go!)" or "Hijé!". But we more use "Hijé!", if it's a horse.
And I think, that "Hüa!" is something like "Hijé!". Asuka is right. It doesn't make any sense. :3
Actualy, I think, I did something like this to my dad, when I was little. :)
Awwww, I wanna take all of them home.
And, LOL Maki-chan! So, secret agents, huh?
Oh, and Eri's lunch was really something else... Actually, I expected something like this, when I saw that matryoshka lunch box... hehehe