Question

All of us, our family and the Chinese guests, stopped eating to watch the activities of the Gleasons. I wanted to giggle. Then I caught my mother’s eyes on me. She frowned and shook her head slightly, and I understood the message: the Gleasons were not used to Chinese ways, and they were just coping the best they could. For some reason I thought of celery strings.
What part of the plot is revealed in this excerpt?