YOU SAID:

once there was a mouse who ate cheese

INTO JAPANESE

かつてはチーズを食べたマウスがあった

BACK INTO ENGLISH

There was a mouse ate the cheese used to be

INTO JAPANESE

マウスを食べたチーズの使用があったこと

BACK INTO ENGLISH

It had a mouse eating cheese with

INTO JAPANESE

それはチーズを食べるマウスを持っていた

BACK INTO ENGLISH

It had a mouse eating cheese

INTO JAPANESE

それはチーズを食べるマウスを持っていた

BACK INTO ENGLISH

It had a mouse eating cheese