1. Only one part of our house gathers hair on the floor.
  2. It does not appear to be hair from any of our family members. Ew, the fact that I even had to think about that, ew.
  3. The floor does not appear to be growing hair, because it is never attached.
  4. Only remaining source, the only remaining possibility.
  5. There's a Sasquatch in our vent.