[IR]rationnel is an audio-visual interactive installation commissioned by the Centre des sciences de Montréal and produced by Molior. It was made for the festival Eureka! and one of the challenges was to use some of the images submitted to the scientific imagery competition. I imagined a 2D virtual space that was connected to our world via computer vision. It responded with sound. The participants could interact with it simply via their presence or gestures. It was a symbiosis between humans and machine. It was easy to play and somewhat challenging to master.