Many people know literature only as something written. The concept of oral literature is important in cultural anthropology but for the vast majority it is completely unknown.
When we speak, we do not always speak freely but we are within certain traditions. For example when we tell traditional tales, that is oral literature–some philologists, cultural anthropologists and others collect and write down oral literature and thus turn it into written literature. Also when we create tales ourselves, we usually do it within some tradition, making use of well-known schemes which form part of oral literature.
Also proverbs belong to oral literature. If I say: "All that glitters is not gold", I do not say it as a spontaneous sentence but I repeat somethng with a tradition. I can even say only the first half and whoever listens to me, knows the second half if they are familiar with that part of oral literature.
The greeting formulas are an important part of oral literature. In some cultures there are long rituals of obligatory sentences for greeting. For example in Wolof (in West Africa) in fixed moments one includes as a part of a long ritual the other's name and one asks the other how he or she is, and everyone will answer that they're good irrespective of their actual states. Also in Spanish and Catalan it is very common to ask "How are you?" within a greeting. In German the same question is used but unlike in Spanish and Catalan it is not common when talking to someone one is meeting for the first time. In English the question "How do you do?" does no require an answer but the repition of the same question.
Traditional allegories are another part of oral literature. When we speak of a black sheep, it is unnecessary to explain it to adults because they already know this allegory. In large areas of Earth people understand us when we say "the heart" and in fact do not refer to the part of the body named thus but to the emotions and particularly to love. In Indonesian this allegoric function is taken by the liver (in Indonesian hati) and not by the heart. In the satirical novel "Voyage to Kazohinia" by Sándor Szathmári the traveller first in a group of people does not feel understood because they do not understand his allegory of the heart. Afterwards in another group he himself does not understand the allegory when they speak of the lungs with the same figurative sense. That is very normal that we have difficulties to understand allegories of other cultures.
A great deal of symbolic meanings can be found in the verb "to eat". When someone says in Irish: "He eats the neighbours", it means: "He backbites the neighbours." When someone says in German: "I like you for eating you up", it means: "I like you a lot." In different Papuan languages when someone threatens: "I'll eat you up!", that actually means: "I'll bewitch you!" Many travellers did not understand the allegory and thought that was a threat of canibalism. There is a tendency of humans that we take literally what people of other cultures say and think they cannot symbolize like we do. That often causes misunderstandings in intercultural contacts.