How can parallel lines not be parallel?
It’s Fred! Hurray! At last some sanity on the show, as Fred explains how his bathroom tiling is going.
Fred’s been doing a bit of DIY in the bathroom, putting up some new tiles. Unfortunately, his design looks like this:
Hmm. All a bit wonky, don’t you think?
Gareth certainly isn’t convinced. The lines of tiles just don’t look parallel – it looks like the tiles themselves can’t be square.
But the tiles are square, as Fred demonstrates by sliding the rows back into a normal chequerboard arrangement. How can this be?
It’s an optical illusion, of course. It’s called the ‘Café Wall Illusion,’ because it was first spotted on the wall of a café frequented by a psychology professor who had a particular interest in optical illusions. You’ll find more about this illusion at WikiPedia, and here’s a nice interactive version.