What does he mean by "Bless you" here?
Native speaker’s answer
Rebecca
"Bless you" is something that is said after someone sneezes. According to the Library of Congress, this saying may have originated during the bubonic plague, where the symptoms were coughing and sneezing. They hoped that if you said "Bless you" or "God bless you," it would prevent the person from dying. We still use this saying to this day.