YOU SAID:

He grumbled something unintelligible and hung up.

INTO JAPANESE

彼は理解できないことをつぶやいて電話を切った。

BACK INTO ENGLISH

He muttered what he could not understand and hung up.

INTO JAPANESE

彼は理解できなかったことをつぶやいて電話を切った。

BACK INTO ENGLISH

He muttered what he could not understand and hung up.