You can tell what movie is playing in a cinema from the audience's breath

Particularly during funny and suspenseful scenes

Well this is a bit weird. Researchers have found out that it's possible to tell what film is playing in a cinema by merely sampling the air coming out of the theater.

A team from the Max Planck Institute for Chemistry and Johannes Gutenberg University analyzed the contents of the audience's breath from the ventilation system while they watched a movie.

During tests on 16 different films, shown multiple times to audiences of different sizes, the researchers found that the chemistry of the air changed as different types of scene played out. Even more impressive, they could then recognize characteristic chemical patterns over time and associate them with particular movies - even when the crowd changed.

"The chemical signature of 'The Hunger Games' was very clear; even when we repeated the measurements with different audiences," said Jonathan Williams, group leader at the Max Planck Institute for Chemistry. "The carbon dioxide and isoprene levels in the air always increased significantly as the heroine began fighting for her life"

Isoprene is one of more than 800 different chemical compounds found in breath, but the exact physiological process that creates it is unknown. The team believes that the spike results from moviegoers tensing up and breathing faster when watching scenes involving suspense.

Clear Signal

Other compounds signaled different types of scene. Funny sections resulted in different molecular traces. "In statistical terms, we got a clear chemical signal for humorous and suspenseful scenes, and were able to identify these even without seeing the movie," said Jörg Wicker, who developed the evaluation algorithms.

The team believes that there could be practical applications for the finding - particularly in the advertising industry. By studying the chemistry in the ventilation system, theaters can quickly and objectively measure how large groups of people react to emotional stimuli without going through lengthy surveys.

Their next goal? Assessing chemical traces from audiences watching Star Wars. In the meantime, the team has published its findings so far in the journal Scientific Reports.