Am I the only one with a problem, seeing these two images (second one can be found inside) as one continuous spiral line? In reality, both of them are constructed out of many concentric circles, yet the pattern filling their background somehow prevents us from seeing the image in it’s true nature. I wouldn’t expected anything less from great optical illusions, like these two! There were many similar examples in the past, but these are my favorites for now. Which one worked better for you? I liked the first one better, but in my belief the illusion works better with second example. If you have few more minutes, I recommend you check the Spiral Tag, and see many more where these came from!
Update: In the first image, I was referring to pink line only.