What is the ground covered by?
The ground is covered by the dirt.
    src        edge_attr  dst
0     0       covered by    9
1     3  to the right of    7
2     3  to the right of    4
3     3  to the right of    5
4     4   to the left of    3
5     5   to the left of    3
6     6   to the left of    9
7     7   to the left of    3
8     9         covering    0
9     9  to the right of   10
10    9  to the right of    6
11   10   to the left of    9