A luduan was a beast which could detect truth, in the mythology. Thus in the Qing dynasty, rulers such as the Emperor Qianlong would surround his throne with ''luduan'' in order to properly subdue his subjects. In the adjacent image, the ''luduan'' were incense burners. The enamelled charcoal braziers next to the Dragon Throne may not actually have been so close, but since Forbidden City in Beijing is at the latitude of Chicago, the Emperor may have required the braziers for comfort.
Above the throne, not shown in the image, was secreted a box in which the name of the next emperor was written. This was the way that Qianlong himself learned that he was the successor to the Dragon Throne.