You use your mouth when you see a Chinese person and you sigh. You sigh so loud that it’s practically a roar coming out of your mouth. Chinese people and Chinese things make you sigh because it reminds you of when you stayed in China and it brings up memories. The sigh is a sigh of nostalgia.
Your favorite Chinese thing to do is tan (たん). You can wander around without your shirt on and tan all day. No one will sigh or scoff at you, it’s perfectly acceptable. The Chinese just love to get their tan on.