What do the number and the train car have in common?
The color, both the number and the train car are black.
    src        edge_attr  dst
0     2  to the right of   10
1     2  to the right of    8
2     3  to the right of   10
3     3  to the right of    8
4     5               in    9
5     5   to the left of    6
6     6  to the right of    5
7     8   to the left of    2
8     8   to the left of    3
9     8   to the left of   10
10   10   to the left of    2
11   10   to the left of    3
12   10  to the right of    8