1. That is not walking.
  2. Maybe it's dancing?
  3. Sex ...? But so much aggressive and multi-origin thumping.
  4. Rearranging the living room at 11pm?
  5. Sex.
  6. No that can't be sex. If so it sounds dangerous.
  7. What if one of them cut up the other one and is putting them in a suitcase like in Rear Window?
  8. Invasion of elves in rollerblades.
  9. [time-honored New York move of bashing ceiling with broom]