Ball insects (Armadillidiidae) are a favourite with children, because they roll into a perfect ball if touched, and they don't bite. To the naked eye, they look just grey, it was a surprise to see they have patterns when I enlarged the photo.
Love it. Once when I was on holiday in a hotel room, I picked up what I thought was a perfectly round brown bead with pretty ridge markings, maybe fallen from someone's necklace. And then I shrieked in shock when it started uncurling in the palm of my hand!
Ian