YOU SAID:

i heard this one time that people decided to eat people so that the people who were eaten by the people were eating people while being eaten by the people

INTO JAPANESE

あるとき聞いた話ですが、人は人を食べることに決めたので、人に食べられた人は人に食べられながら人を食べることになるのです

BACK INTO ENGLISH

I once heard that people decided to eat people, so people who were eaten by people ended up eating people while being eaten by people.

INTO JAPANESE

人は人を食べると決めたので、人に食べられた人は人に食べられながら人を食べることになった、という話を聞いたことがあります。

BACK INTO ENGLISH

I once heard that people decided to eat people, so people who were eaten by people ended up eating people while being eaten by people.