How does salt+watermelon=STRONGEST?

Catloaf said:
How does salt+watermelon=STRONGEST?

I think it's because she took it from Kanji

I still didn't get it when it was Yotsuba with the fish and riceball. It just seems like a non-sequitur/kid thing to do.

It's possibly a reference to Cirno's item being a watermelon and her catch phrase being "I'm the strongest!"

I thought it was a reference to Kanji being the strongest character..and now Nanako is strongest.

It's because watermelon and salt go so damn good together.