Saliva

Just consider the saliva in the mouth and see the wisdom underlying it. It is so composed as to ensure constant flow to keep the throat and the palate moist, not to allow dryness therein that they may lead to death. Without it the food would not he chewed nor would it flow down. All this is obvious and supported by observation. And know that this fluid is derived from food and getting down aids the action of the gallbladder. ¹

References:

1. Tradition of mufaddal, dictated by Imam Ja’far al-Sadiq to Mufaddal (Mufadhal) ibn `Umar[↩]

[Quran Chapter 30:5-6] 5. In Allah's support. He supports whomever He wills. He is the Almighty, the Merciful. 6. The promise of Allah—Allah never breaks His promise, but most people do not know.