Very often, I see a "chain reaction" in people coughing in an exam hall. One person coughs and many follow. It's not necessarily the person closest to him who coughs, it can be someone sitting far away. This doesn't just occur in this setting but also in other situations, such as in public spaces. I was wondering if this is a reflex which has evolved over time as a means of protecting our body from pathogens and harmful chemicals in the air.