Things you see but you don’t see

Everyone will instantly recognize this snap of the Empire State Building in Manhattan:

But if you’ve got sharp eyes, you could in theory notice something else – but it seems nobody ever does. If you look closely, you’ll see that every building has a little tiny box on its roof.

There is a law in Manhattan that every building must contain a cistern of water on the roof that can be released and gravity fed in case of a building fire.

The truly amazing part is that nobody ever notices these little boxes until they’re told about them – but as soon as you know they’re there, you can’t help but see them!