This sentence is using a simile by comparing the guy's belly's fullness to the tightness of a drum. We know it is a simile that is being used being it is using one of the key words that makes it a simile (like or as) which is as.
Satrapi have said so many things regarding the disparity or the differences between the classes before and after the Iranian Revolution. Some of the parents were not allowing their sons or even maybe their daughter to come and attend the demonstration when Shah was taking control of everything.
