This is a stupid little scene I've had stuck in my head for years, so for anyone who watched it and was completely confused here ya go! Or, if you haven't seen Assasination Classroom, go watch it!
Music
NCS Chill Music
Free Chill Lo-Fi Music (For YouTube Videos) - "Colorful Flowers" by @tokyowalker4038 🇯🇵
Mata Kimi Ni Aeru Hi (Assassination Classroom S2E2 ED)
https://www.youtube.com/watch?v=ZvdxQwHaX6I
Explanation (S;G OST)
https://www.youtube.com/watch?v=HSiVHU7ISK4
Wigner Seitz Explanation
https://www.youtube.com/watch?v=gYX90XMdXqM&list=PL2Kh6IaMYK0-ET0EPU3nKC869HFHzWpck&index=91