A few years ago, the city council of Monza, Italy, barred pet owners from keeping goldfish in curved bowls. This law was meant to protect the poor fish from a distorted nature of reality, since bent light might show them an odd portrayal of their surroundings.

Hawking and Mlodinow bring up the incident to make the point that it is impossible to know the true nature of reality. We think we have an accurate picture of what's going on, but how would we know if we were metaphorically living in a giant fishbowl of our own, since we would never be able to see outside our own point of view to compare?