I'll start by saying that Josephine has made incredible progress since we rescued her - she used to bite and scream and hiss and scratch, all the time, and now she's quiet and cuddly. However, I've NEVER heard her purr. She can lay in my lap and get her head and chin scratched and look as happy as can be, but I've never heard her purr once. Do some cats just not purr, or is she still adjusting?