Explain the following statement "digestion begins in the mouth"

It tells you that digestion actually begins in the mouth and not stomach. The salivary gland in the mouth secrete saliva which contain enzyme known as alpha- amylase which start the digestion of carbohydrate. Also the chewing and lubrication of food in the mouth make digestion easier, because it make swallowing easier.

The mouth is the first step in the digestive process because you need your teeth to chew the food. This breaks down the food you eat so it can move on to the next process.
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The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)