When a fan recently asked Harry Potter author J.K. Rowling via twitter if her new show ”Cursed Child” would make him cry, Rowling responded that if it didn’t, “we’ll be checking your vital signs.”

While Rowling most likely didn’t mean this literally, the ability to check your vital signs as a way to gauge your reaction to a film, or in this case a play, is already a reality.

Scientists in Germany, at the Max Planck Institute for Chemistry and at Johannes Gutenberg University, have analyzed the chemical compounds found in people’s breath to determine their reaction to a range of films, one of which happened to be “Hunger Games 2.”

In the study,  which appears in Scientific Reports, scientists looked to see differences in the exhalations of people who were watching either a funny or a suspenseful film. Based on the breath analysis of 9,500 viewers to 16 different movies, scientists were able to identify whether the breather found a scene comedic or tense. Although it’s still not possible to specify all the compounds in the breath, the analysis included detection of higher and lower levels of carbon dioxide, acetone and isoprene. Variances in these levels, they suggest, may be attributed to “breath holding” or cortisol production during tense scenes.

An article in the Wall Street Journal speculated that such analysis could be used to directly survey a crowd’s reaction, so as to anticipate success of a new film. In the future, marketers, along with tracking your likes on Facebook and your online purchases, could data mine the very air you breathe. The collection of our exhalations, described by the researchers as objective and non-invasive assessment of a human group response, should perhaps make us take pause–along with a very deep breath.

Illustration: Pete Ryan