Salem

I started playing 10 days ago, today I was doing different things inside my fences and I noticed a patch of ground that was a square with the borders made of human skulls and the inside like a pile of mixed bones.
I took a screenshot, I used ''Dig'' , one shot and it was gone, what is it?

http://game.salemthegame.com/mt/ss/9e8b ... 1bdec73e30

When you were paving you had a bone in your inventory, It works as a paving material.

http://salemwiki.info/index.php/Paving

Yeah, I just figured it out, at first I thought there was some curse hehe.
Thanx