This sketch is created with an older version of Processing,
and doesn't work on browsers anymore.
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int[][] d=new int[49][2];int i,a,b;void draw(){for(i=0;i<49;i++){stroke(99);point(a=d[i][0],b=d[i][1]);stroke(0);point(d[i][0]+=random(5)*(2*int(mouseX>a)-1),d[i][1]+=random(5)*(2*int(mouseY>b)-1));}}