It's a magic trick! It's sorcery! How else can you explain that stick being able to pass through that curved hole? If you showed me the two pieces separately, I would have never imagined them to actually fit one another so seamlessly.
This was an exhibit at the Science Museum in Valencia, Spain. The basic trick is that something that looks straight can actually act (or appear, to our eyes) curved (and vice versa) depending on the angle.
And yes, I'm aware of the word choices to describe these two parts.