0Itadakimasu and Gochisousama:
There is a custom to begin and end your meal with a greeting that expresses your gratitude toward the food itself.
There is a life force that exists within food, and, as you begin to consume that force, you say Itadakimasu (literally, "I humbly receive").
Saying Gochisosama (literally, "It was a feast") after the meal is a cultural given. Whether you say it out loud or not depends on the situation. When you are at a quiet place or by yourself, wordless appreciation is just as good as saying the phrase out loud.
They are simple words, however very important to think about appretiation of food.
