His active feet. Jacob has attached yellow bee-bands to prevent any bees from crawling up his legs. Before he came to the cave, he did catch some type of foot fungus, probably in a public shower, which has flaked his walking skin, and it is just as well for the pristine ecosystem of this faraway planet that Jacob has so well protected his feet from the stone, (that yellow-band, big-shoe protection works in reverse). Future scholars will be able to collect floor stone samples without fear that the archaeological sediments of original-resident DNA have been disturbed by the dust of foreign growths brought by astronuts like this one.     They weren't directly visible to sight. But I knew they were there.