Active at night and rest in day.
1400 years ago people thought that all animals rest at night. However today we know that this is false. Some animals are active during the night and rest during the day.
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Wikipedia, Nocturnality, 2019.
However the Quran said that there are creatures that rest at night as well as creatures that rest at day:
[Quran 6:13] To Him belongs whatever rests in the night and the day. He is the Hearing, the Knowing.
Creatures that rest in the day means they are active at night. No mistakes in the Quran.
How could an illiterate man who lived 1400 years ago have known about nocturnal animals?