diff --git a/examples/snake.rb b/examples/snake.rb
index 73dad9d..a00d501 100755
--- a/examples/snake.rb
+++ b/examples/snake.rb
@@ -6,13 +6,13 @@ include OpenCV
 
 puts <<USAGE
 usage:
-  left-click: set point
+  left-click: set a point
   right-click: do snake
 USAGE
 
 window = GUI::Window.new "snake demo"
 image = CvMat.new(256, 256, :cv8u, 1).clear!
-image.circle!(CvPoint.new(128,128), 40, :color => CvColor::White, :thickness =>  -1)
+image.circle!(CvPoint.new(128,128), 40, :color => CvColor::White, :thickness => -1)
 display = image.GRAY2BGR
 
 window.show display
@@ -22,7 +22,7 @@ points = []
 window.on_mouse{|mouse|
   case mouse.event
   when :left_button_down
-    display[mouse.x, mouse.y] = CvColor::Red
+    display.circle!(mouse, 1, :color => CvColor::Red, :thickness => 2)
     puts "set point (#{mouse.x},#{mouse.y})"
     points << CvPoint.new(mouse.x, mouse.y)
     window.show display
@@ -31,10 +31,11 @@ window.on_mouse{|mouse|
       puts "please set more point!"
       next
     end
-    points = image.snake_image(points, 1.0, 0.5, 1.5, CvSize.new(3, 3), 100)
+    snake_points = image.snake_image(points, 1.0, 0.5, 1.5, CvSize.new(3, 3), 100)
     display = image.GRAY2BGR
-    display.poly_line!(points, :color => CvColor::Red, :is_closed => true)
+    display.poly_line!([snake_points], :color => CvColor::Red, :is_closed => true, :thickness => 2)
     window.show display
+    points.clear
   end
 }