The study highlighted the second Hunger Games movie, during which CO2 and isoprene levels gradually rose through the movie, as expected as people sat in the theater for longer, but also peaked during tense moments-Katniss’ dress catching fire, the final battle beginning. Jumps in CO2 probably correspond with excited exhalations, while isoprene jumps could be caused by holding one’s breath or fidgeting muscles.

— Read more at Why People Can Literally Smell Your Fear in Movie Theaters at Esquire, or read the original study Cinema audiences reproducibly vary the chemical composition of air during films, by broadcasting scene specific emissions on breath at Nature.