There are four liquids in the head: sweetness in the mouth that mixes well with food and drink; stickiness in the nose that prevents dust from entering; saltiness in the eyes that prevents dryness; and sourness in the ears that protects from insects. The Qur’an invites all to ponder:
‘On the earth are signs for those of assured Faith.
And also in your own selves. Will you not then see?‘ [Qur'an 51:20-21]
from:
Don’t Be Sad, Aaidh ibn Abdullah al-Qarni, pg. 329
