It all depends on local custom. In Australia, a fly in one’s soup results in it being sent back to the kitchen and a row with the management.
In England, the head waiter quietly, daintily, fastidiously extracts the fly and removes it beneath a serviette.
In France, the soup is eaten, the fly left high and dry on the side of the bowl.
In the Orient, the fly is eaten first and washed down by the soup.
In Scotland, the fly is shaken over the bowl and carefully wrung out. Then the soup is consumed.
And there are places where the diner stares into the bowl and complains. “What’s this? Only one fly?”