     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"

      S.circle {
        class: "head"
        cx: head, cy: y
        r: half
        fill: "#00aa00"
      }
    ]
  [
    S.rect {

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