My cat sometimes doesn't notice the adult ones when they are so very still

I doubt that 😄 It's impossible for cats not to notice something. They are only pretending. My cats also pretend not to see the hedgehog in the garden. 😎 It's because they don't know what to do with it. And your cat probably knows it can't catch up with the rabbit, so it sometimes pretends not to see it. One can die of laughter with their acting. 😂
You are welcome!