あの時の鰻が、兵十が病気の母親に食べさせようと必死に捕ったものだったと知ったため

A few days later, Gon witnessed the funeral of Hyoju's mother. Hyoju had only his elderly mother, and that eel caught in the river had been desperately caught to feed his dying mother to give her strength. Realizing the gravity of his prank, Gon was devastated by intense regret and a guilty conscience, thinking, 'What a terrible thing I have done.'