I've been away for a few days and not posting, so I'm just putting this up by way of saying that I'm back into posting from today. This is one of the most amazing optical illusions I've ever seen. It's particularly amazing because it seems at first glance to be obvious what it is. And yet... if viewed from a certain distance, with gaze maintained at the wrong focal length, and under certain circumstances it transmogrifies into something completely unexpected. It takes persistence, but it's worth it in the end. It took me ages, and some eye strain to get the effect, but if some commenters have an easier shortcut, I'd be interested. Also if anyone knows the origin of the illusion I will attribute it properly (it came to me via an email which was forwarded many times). Good luck!
