The composition of theatergoers' breath fluctuates along with movie scenes, according to a study published this week in Nature’s Scientific Reports. Researchers from the Max Planck Institute for Chemistry and Johannes Gutenberg University found that they could reliably map the chemical patterns of a movie as it progressed through heart-racing scenes and calm ones. During The Hunger Games, for instance, carbon dioxide and isoprene levels increased whenever Katniss was fighting for her life. The researchers think isoprene levels correspond with suspense.

Their findings come from more than 9,500 participants who viewed 108 screenings of 16 different films. The air pumped into the theater wasn't manipulated in any way, and the researchers monitored the outflow of air for more than 100 gas types. They suggest their findings could help measure anxiety in medical patients, as well as the reactions of consumers to advertisements.