tldr: integer vs half integer spin. Fun fact, matter can actually have integer spin as well. For example Helium-4 has integer spin, -1/2 + -1/2 + 1/2 + 1/2 fo

tldr: integer vs half integer spin. Fun fact, matter can actually have integer spin as well. For example Helium-4 has integer spin, -1/2 + -1/2 + 1/2 + 1/2 for a total of zero. And that's why it can act like a superfluid.