Rabbit and cat psychology?

hi I have a cat felix and he is a big softie and he loves being loved and cuddling. When he goes out he always gets attacked and never fights back,, I think hes harmless. and yesterday I just rescued a rabbit that hadn't been fed for 15 days and was filthy and full of wee. At first felix was just curious around the rabbit but now he just sits and does his own thing. He doesn't seem bothered about the rabbit. Do you think he just doesn't mean any harm or is he playing it cool until there alone together?? Felix once didn't mind when we got a kitten so maybe he won't mind a rabbit. do u think he's a clever cat binding his time or will he be nice? Also what does it mean if his tail is straight up towards the ceiling and moves now and then ?? X