When the leg sweeps across the carpet, electrons are brought into the leg.  The electrons repulse each other with an inverse force law,
see coefficients in Electron.js.  The body is modeled as a closed polygon.  The polygon was created by using DebugUtils.js to sample points
in the coordinate frame of the ScreenView.  When enough electrons have amassed (depends on the distance of the finger to the doorknob), it creates a spark.
The electrons travel along force lines to the finger.  The force lines can also be sampled using DebugUtils.  Electron positions are computed
in a body with unrotated appendages, and mapped in the view to the positions corresponding to the rotated appendages.

Sam Reid
10-7-2013