Are we being led by models from the past

When I was young, someone asked me why a trombone’s slide didn’t just go through the player’s mouth and out the back of their neck. It baffled me at the time! Now I understand that there are two parts to the slide: the inner slide, which stays put, and the outer slide, which moves back and forth. It’s a neat trick of design, but as a child, that illusion felt very real.

You might recognise the drawing above—do you see a girl or an old lady? It’s fascinating how our initial interpretations can lock us into a particular way of seeing things. Once you’re told there’s another perspective, reversing your original view can be surprisingly difficult.