I feel sure they want something.
Homer undoubtedly wants food.
Fifi has discovered that there is an outside and she wants to go there. Since she has been an indoor cat all her life and is the scaredy-est cat in the world, there's no way that's going to be allowed. But she has made two escapes when the door has not been closed securely, fortunately cornering herself in the garage. She is lured back in the house by the rattling of the kitty treat container.