In the video clip this blog entry is based on, Master Roshi is trying to convince a girl he is young. He does this by reacting to the girl’s statement that “Your grandsons helped me” by responding “Those aren’t my grandsons, those are my younger brothers”.
Two significant things happened in reaction to Master Roshi’s claim that Crillen and Goku are his brother’s.
First, Goku, Crillen and the girl all fall to the ground.
They do not fall in a haphazard or random way though. Each of them fall to the ground chin first,
with their legs up in the air.
After this happens, Master Roshi tells the girl, “that was a good joke wasn’t it?”. Then they all laugh it off. As they laugh, Master Roshi is facing the girl and his right arm is holding the back of his head.
You will also notice that the girl has her handkerchief covered hand to her face.
Both of these characters make these motions for a specific reason. If you understand kung fu principles, then you understand why these particular motions are made by an embarrassed person.
It has nothing to do with psychological reasons. It has to do with the basic structure of the body and how various structures within the body react to energy.