Responsible for balance.
1400 years ago people thought that ears were responsible for hearing only. However today we know that ears are also responsible for balance.
Providing balance, when moving or stationary, is also a central function of the ear. The ear facilitates two types of balance: static balance, which allows a person to feel the effects of gravity, and dynamic balance, which allows a person to sense acceleration.
Wikipedia, Ear, 2019
The inner ear is responsible for balance. However 1400 years ago the Quran described people who got knocked out by blows to their ears:
[Quran 18.11] Then We hit on their ears in the cave for a number of years.
In Arabic "Darabna ala Athanihim فَضَرَبْنَا عَلَىٰ آذَانِهِمْ " means we hit them on their ears. If you see these people you will think they are awake however they actually couldn't wake up. If you are asleep anything can wake you up however if you are knocked out then nothing can wake you up. Just watch a boxing match and see the difference. Since these people couldn't wake up then they were knocked out by blows to their ears.
How could an illiterate man who lived 1400 years ago have known that you could get knocked out by your ears?