Today I learned something sensational about cats. Bringing my cat to the vet I asked why somethimes while looking each other in the eyes he slowly closes them all the way, then opens them back up to the halfway position to gaze at me once again. I always thought he was sleepy but the vet reassured me saying this is a cat way to say I LOVE YOU!
Some cats will perform a variation of this, starting with their eyes open, then closing them halfway while making eye contact with you. On occasion, a cat will even perform one of these actions with only one eye, winking in a charming manner.
But most cat behavior experts agree that this gesture is actually part of your cat's communication arsenal.
It means that he is relaxed, happy, and content, and he wants to convey that information to you. It's like a kitty kiss! Telling you "I'm watching you, but I'm not vicious to you, trust me", he’s doing a gesture of trust and pacification. At this point it would be polite answer the cat's wink: in this way you tell him that you know that he is there, that he is watching you and that you too are not a threat to him.
You can try doing the same approaching a wild cat: try to wink at it and watch its reaction.
xoxo from me and my cat Eros!