About circles and spheres. The scene is actually addressing a bigger
issue. For mathematicians, spheres are a general notion which also applies
to circles (spheres in 2D). Spheres embedded in our 3 dimensional space are
2 dimensional objects. They are the boundary of 3-balls, which are 3-manifolds
with boundary. I liked in the movie to see some familiar faces like
Mal and Wash from the Firefly movie and Midge from "The Marvelous Mrs Maisel".