The jar on the coach

Original fiction extract.

My uncle opened the jar only to check that the lid had been properly tightened. That was his explanation afterwards. At the time, a sharp smell of pickled onions escaped into the coach and began taking seats without asking. The woman across the aisle turned towards the window. A boy behind us lowered his packet of crisps and sniffed. Uncle closed the lid, but the smell had already settled among the coats. He held the jar between his knees with the formal dignity of someone who had brought a difficult guest.

Choose one example from the extract and explain how the writer uses language to suggest the effect of the opened jar on the passengers. Use your own words in your explanation.