This line divides the real upper side or back from the real lower side or belly of the fish.

这条细线将比目鱼真正的上方（或背部）, 与下方（或腹部）一分为二。

If you’re reporting about the sun rising in the east, you do not need to hear the other side because there’s no real other side.

如果你在报道太阳从东方升起， 你不需要听到对方的声音，因为没有真正的另一方。