Minecraft wiki entry for Swamp_hut, associated text: Additionally, witches can spawn on any block within the 7×7×9 (x×y×z) area that constitutes the hut (this is the size of the roof and one block over the porch, from one level below the floor of the hut to two blocks above the roof). Cats can also spawn within this area. However, they require a grass block to spawn on. In Java Edition, any other cats to spawn within the swamp hut (from spawn eggs and commands without cat type set) always spawn as black.