From Nico Nico Douga Original Title スペランカー先生のパーフェクトざんきすう教室を歌ってみた http://www.nicovideo.jp/watch/sm8461698 ④(shi) 4 is read as Yon or Shi in Japanese. And 死(death) is read as Shi too. So, 4 is understood as an unlucky number. His soul is drained from his body at taking a picture Over one hundred yeas ago in Japan, they think cameras drain thier soul.