In 1999 I began to study the means by which dynamic graphical lines could convey a plausible sense of physicality. After some experimentation I developed a model for representing the underlying structure of "physical" lines, in which a finite-element, mass-spring-damper simulation is composed of virtual particles connected by alternating linear and torsional springs. The model has the effect of simulating the tensile properties of thin physical filaments, such as hairs or twigs. I used this physical model to create a series of reactive drawing systems, including Floccus. In Floccus (the name is a Latin term for "hairball"), ductile filaments drawn by the user swirl around a shifting, imaginary drain centered at the user's cursor. These filaments--torn by conflicting impulses to simultaneously preserve their length, yet also move towards or away from the cursor--find an equilibrium by forming gnarly, tangled masses.