Applications of the quartic curve $x^2y^2-1=0$?

Question

The quartic curve $x^2y^2-1=0$ is equivalent to the union of the hyperbolas $xy-1=0$ and $xy+1=0$, i.e., it's a rectangular hypobola superimposed with a copy of itself rotated by 90 degrees. Does this curve have a name? Are there any natural applications? I like this curve pedagogically as a simple example of implicit functions and implicit differentiation, but it's always more fun to have a good application to point to. The appeal for me is that unlike $xy=1$, it can't be expressed as a function, and yet each of its branches is just as easy to analyze as $xy=\pm 1$.