Nothing other than the basic model bone. You don't get much choice about that one. If you load up the projects, you'll see the problem. Oddly, it's not deterministic. I got the marbles to roll around in the jar in the successful project, but later, I loaded the same project and the marbles fell through. Re-run the sim, some fall through, re-rerun again, it works, fine. Try again and get more random results. Physics isn't supposed to work that way.