* Independent: Cats are often described as being aloof and self-sufficient. They don't always need human interaction and can be content with their own company. This "half out" aspect suggests a sense of detachment and being on their own terms.
* Unpredictable: Cats can be quite enigmatic, switching moods quickly and seemingly acting on their own whim. The "half in" element reflects their ability to engage with you at times but also to withdraw just as suddenly.
* Mysterious: Cats have an air of mystery about them. Their curious nature and secretive habits can make them seem like they are always holding something back. This "half in and half out" feeling adds to their mystique.
Ultimately, the saying is a humorous way to capture the complex and often contradictory nature of cats. They can be cuddly and affectionate one minute, then aloof and independent the next. This duality is what makes them so fascinating and endearing to many people.