The answer to that is as easy as chewing cud. You chew your food until the food in your mouth is made liquid!
One of the main secrets and fundamental rules to increasing your metabolic rate, is to support the processes of digestion thus leading to good absorption of the nutrients contained within the foods and liquids you consume. And the first action we must all adhere to to initiate effective digestion of what we consume is the simple action of chewing.
Understand this... The body can only metabolise foods that are in a liquid state. If the foods you eat are not in a liquid state when you swallow them, the whole process of digestion is hindered from the very beginning.
Even liquids you consume (like your green smoothies) need first to be activated by the first of the digestive fires, your mouth saliva. Not so much to break up the solids as they're already chopped up, but the act chewing activates the secretions of saliva in the mouth called ptyalin and that saliva is mixed with your smoothy so your body can digest the goodies.
That states, "It's not what you eat, its what you absorb!"
The physical act of chewing also stimulates energy pathways (meridians) that are situated around your temporomandibular joint (your jaw bone), which are related to your first organ of digestion... your stomach. When you chew, the physical action utilises many muscles that are situated around your jaw and skull.
From there your body can recognise that nutrition is coming in turning on the digestive processes of the other organs of digestion your liver, gall and pancreas. Every organ of digestion within the human body produces its own individual saliva but the whole process can be and is hindered, if in the very first instance, the first digestive saliva (the saliva produced in the mouth) is not activated/turned on!
Even the absorption of water requires it to be first impregnated with mouth saliva.
That's why when you drink a glass of water you keep your jaw closed and draw the water through your teeth. As soon as you start to swallow with your teeth closed your mouth will make saliva.
Try it! Close your teeth and swallow and feel your mouth secrete saliva from your bottom jaw bone and under your tongue. It's a beautiful system that is so simple and so misunderstood that if not adhered to can create problems within all the organs of digestion.
So in a nut-shell, when you eat food... CHEW your FOOD INTO A LIQUID BEFORE SWALLOWING!