Zawa Zawa ざわざわ

The word zawa zawa ざわざわ is a sound effect found in the gambling manga Tobaku Mokujiroku Kaiji 賭博黙示録カイジ, and in parodies of it. It normally shows up in tense, cold-sweat-breaking, anxiety-filled situations, which are common in the gambling series.

Awkwardly, zawa zawa is an onomatopoeia, and not a non-onomatopoeic mimetic word like gogogogo ゴゴゴゴ from the JoJo's Bizarre Adventure. That is, in the anime adaptation, you get to hear the zawa zawa sound, and you assume the characters can hear it too.

Where Does It Comes From?

What emits the zawa zawa sound exactly is a mystery wrapped in enigma.

It's hypothesized that it could be a sound of commotion, coming from the background characters watching the anxious gambling from afar and whispering at each other. But the sound effect also shows up in scenes where two characters are sitting alone, with no audience watching them.

Another hypothesis is that it could be sound of their hearts feeling tormented in their chests, but in that case it'd make more sense as a non-onomatopoeic ideophone and not as a literal onomatopoeia. A heart making a zawa zawa sound is just weird.

So nobody knows for sure where in the world the sound is coming from, what or who is emitting it, or why, all that's known is when it happens: in anxious scenes like the gambling ones, or the ones where the character has to strike a deal with someone.