This is situational irony because in the scene the cobra slithered over the hostess's feet but she didn't react by screaming and being scared. Instead, she reacted by staying calm.
This is dramatic irony because the reader knows that there is a cobra under the table. Only the Hostess and the American knows about the snake while the rest of the dinner party doesn't have a clue about the snake.
This scene shows the theme of how your gender doesn't impact how courageous you are. The hostess reacts by staying calm when the snake slithers over her foot. But the colonel believed that women would always react by being scared in situations like this. But the women were calm and knew how to handle this situation.