Yes, I'm sure it's one of those optical illusions that rely on the brain working in mysterious ways - you see curved lines all over the place that aren't really there as you move your eyes around the image.I've got no idea at all.
I chucked it up as it annoyed the hell out of me and I thought it would be therapeutic to share that annoyance.
That's right - when you're not looking directly at them!The curves appear curtesy of lines of white stones creating the illusion.