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鳴かぬなら 殺してしまえ ホトトギス
(nakanunara koroshiteshimae hototogisu)

鳴かぬなら 鳴かせてみせる ホトトギス
(nakanunara nakasetemiseru hototogisu)

鳴かぬなら 鳴くまで待とう ホトトギス
(nakanunara nakumadematou hototogisu)

The first variation means: "If the cuckoo bird won't sing, kill it." It is supposed to be the way Nobunaga thought.

The second variation: "If the cuckoo bird won't sing, I'll make it sing somehow." - This is Hideyoshi's way of thinking.

And the third variation: "If the cuckoo bird won't sing, let's wait until it does." - is Ieyasu.

И англо-японское объяснение