Why do Aria and Suzu always play the drum and whistle? When Shino explains the school's rules, Aria and Suzu always play a drum and whistle. Why is that? Is this a reference to anything? Or is it just a Seitokai Yakuindomo thing?
no reason. it's a direction.
The measure is "three-three-seven hand clap"(san-san-nana-byoushi in Japanese).
There is no element that indicates the relevance of this direction in "Seitokai Yakuindomo".