The squirrel you see in the picture below is the ground squirrel, also called the squirrel with cheek pouches. What distinguishes this squirrel species from others is that it carries the food that it does not consume right away in the pouches in its cheeks. The squirrel stocks this food for future use.
These cheek pouches are actually loose folds of skin. The interior lining of these folds is bare but not wet, therefore food can be stored in these pouches for a long time without spoiling. These pouches extend to the sides.
To fill these pouches, the squirrel takes an acorn between its paws and cuts off the pointy parts on both ends with its teeth. Then it puts the acorn in one of the pouches and the next acorn in the other. Pouches are filled in this way one after the other. The animal can place four acorns in each pouch. So, the face of the squirrel alters so that we think it is interesting and cute.