Another fine illusion: in this one, the pairs of horizontal lines are all smooth sine curves, despite the appearance of the jagged zig-zags:
It's really hard for me at least to tell that the zig-zags in the light grey region are actually curved. Zooming all the way in may help if you want to check for yourself.
That's all from us at the blog for this week. Next week, we'll be taking a break for the week of the US Independence Day holiday, but we'll be back the week of Monday July 9, reporting from the useR! conference in Brisbane. In the meantime, have a great weekend!