Have you done something in a different country that is completely acceptable in your own, only to find that you offended deeply offended someone? This is what can happen between cultures because manners are different in each culture.
In the United States, belching/burping is considered very rude. Yet in China it is considered a compliment to the Chef. It is a sign that you enjoyed your food. In the United States, giving someone a “peace” sign with your fingers is acceptable, but if you were in the UK and you gave that sign, but with the palm facing the opposite direction, this would be like you were giving someone the middle finger gesture.
There are so many examples of different things that are considered fine in country, but not OK in another. The important thing is to watch what others are doing around you. If you notice that no one publicly yawns, it is probably best to not yawn in public. If you have questions or are unsure if you should do it, it is best to er on the safe side and refrain from doing it.