     x = i*cell_size
     y = j*cell_size
     head = x + length
-    half = width / 2
+    half_width = width / 2
     S.g {class: "turtle"}, [
       S.ellipse {
         class: "body"

      stroke: "#ffffff"
    }
  draw_leg = (x, y) ->
    size = cell_size# * 0.5
    S.rect {
      x: x
      y: y

      S.circle {
        class: "head"
        cx: head, cy: y
        r: half_width
        fill: "#00aa00"
      }
      S.g {class: "legs"}, [
        draw_leg(x+half_width, y+half_width)
        draw_leg(x-width, y+half_width)
        draw_leg(x+half_width, y-3*half_width)
        draw_leg(x-width, y-3*half_width)
      ]
    ]
  [
    S.rect {
