Ever wondered if dogs can actually smell when you are afraid? New research published in the journal Scientific Reports suggests that humans emit certain chemical signatures that might be predictive of our emotions "by broadcasting scene specific emissions on breath." To test this, they studied the air in a movie theater every 30 seconds over the course of 108 screenings of 16 movies involving 9,500 moviegoers, and they watched how the chemical composition of the air changed from moment to moment. The researchers found that suspense and humor off-gas the clearest signals, while other emotions were more "muddled," as Discover magazine reports. One example: levels of the chemicals carbon dioxide and isoprene spiked in the air in correlation with particularly tense scenes in Hunger Games 2.
That seems to make sense, notes Discover's Neuroskeptic blog, given that stress increases the heart and breathing rates, causing us to exhale more CO2. Isoprene, meanwhile, is associated with muscle activity, perhaps from people fidgeting in their seats. The blog, however, has some issues with the study design. Still, the results provide "a whiff of evidence that humans may use volatile chemicals as signals," observes Ars Technica. And while much more research would be needed to confirm that, the authors "note that audience emissions may be useful for evaluating whether movies are truly funny or thrilling." The work and subsequent studies analyzing what we exhale on a molecular level in different moods also could prove useful in advertising and in the development of medical tools that rely on breath. (See how the Supreme Court could be changing breathalyzers.)