This is very subtle animated gif. It was actually generated by code which you could run in Mathematica. This tumblr called archery is full with this kind of stuff.

Here’s the code:

R[n_] := (SeedRandom[n]; RandomReal[])
G[A_, s_, c_, T_, x_] := A*T*Exp[-(x - c)^2/s]

ListAnimate[
 Show[
   Table[
    Plot[
     100 - n + 
     Sum[G[.05, 6, 100*R[n], 
                 Sum[G[1, .01, k - R[2 n], 1, m/100 + t], 
                 {k, -3, 3, 1}], 
                x],
     {n, 1, 100, 1}], 
   {x, -10, 110}],
    PlotStyle -> Directive[Black], PlotRange -> {{-10, 110}, {0, 100.5}},
    Filling -> Axis, FillingStyle -> White, Axes -> False, AspectRatio -> Full, 
    ImageSize -> {500, 700}],
  {n, 0, 100, 1}]],
{t, 0, .95, .5}, AnimationRunning->False]

found at Bruce Sterling