Anyone have any cool lesson ideas for teaching about the layers of the Earth? (ex. mantle, core)

I was thinking maybe we could do some things with candy bars. Looking at a candy bar you don't know what is inside. If you take a knife or better yet jam a straw into the candy bar and take out a sample you can find out what is inside and how it may have gotten there. I'd tie this with the fact that when we look at the crust of the earth it is not so clear what's underneath, but with invesitgations (p and s waves) and drilling to see what other minerals are in our crust scientists can better determine what is inside.

What do you think???