China's bullet trains are known around the world for their fast speed. But given their relatively closed cabins, the use of ventilation systems to reduce the spread of the coronavirus during the pandemic is crucial. At the end of each journey, Liu Chuanhui and Liang Jun, mechanics at the Zhengzhou East Railway Institute, check the ventilation rate, change the filter screen, and clean and disinfect the system to make sure it is working at maximum capacity. If the air conditioning system is considered the respiratory system of the high-speed train, then these mechanics are the "lung doctors."