@11011110 I wonder if we can find before and after photos to compare. *Edit*: Yes, this article has comparison photos: https://www.utoday.nl/campus-life/74074/student-prank-and-artwork-het-ding-exists-50-years I can see why he called it ‘mirrored’ – the transformation applied is equivalent to reflection in a horizontal plane – though it is also equivalent to a rotation.