Here's why:

* Salivary Amylase: Saliva, produced by salivary glands, contains an enzyme called salivary amylase. This enzyme begins the breakdown of starch into simpler sugars.

* Lingual Lipase: While less significant, saliva also contains lingual lipase, which starts the breakdown of lipids (fats).

While mechanical digestion (chewing) also occurs in the mouth, it's the presence of salivary enzymes that marks the beginning of the chemical breakdown of food.