"Oishii" is one of the two Japanese words Jill knows (the other is "naka"). Just how it ties into this business of walking on her hands like the Kayser Brothers from Yakitate! Japan
, I don't know.
I put a lot of effort into recreating a version of the background from Perfume's PV natoreru ni koi shite
so if you'd like a closer look, you got it!