The ViscousDisplay explores the exchange of social information through transient public interfaces. Shaped by principles of 'underground public art', the ViscousDisplay is conceived as a novel mobile communication medium, where messages can be shared in public spaces. Inspired by biological learning systems; the ViscousDisplay learns gestural motions and colors that form along traces of a participant's movements and maps this information onto a flexible display. Because it is made up of inexpensive materials, the ViscousDisplay is also a disposable artifact which may be collected in public spaces. It combines multi-modal sensing, learning algorithms, and a pliable silicone display.