I posted another thread earlier about my cat wanting to go out all of a sudden after a happy year of being an indoor cat. Battersea looked for a scar and say they found one (I'm sure that they looked because she was missing a big chunk of fur on her side) but I've heard that bits can remain. Maybe she was happy to stay indoors this time last year because she was very thin or because the cat downstairs (who I think is male) hadn't moved in yet but she's not actually completely neutered?