A chemical criterion for rating movies
(PHYSorg.com Chemistry)

A measurable criterion now exists for determining the age rating of films. A group of scientists at the Max Planck Institute for Chemistry in Mainz has found that the concentration of isoprene in cinema air correlates with the cinema industry`s voluntary classification of films. Evidently, the more nervous and tense people are, the more variable is the isoprene they emit. This can be used to deduce how `stressful` a film might be for children and adolescents.