I mainly thought they were metal because of being suspiciously shiny and the 'clang' they made as they fell down! The grasper didn't seem to have much of a vacu

I mainly thought they were metal because of being suspiciously shiny and the 'clang' they made as they fell down! The grasper didn't seem to have much of a vacuum hose, either. But metal bricks would be an odd choice --- very heavy and not really good for demonstrations, so I'm quite willing to be wrong.