What is the horse pulling?
The horse is pulling the carriage.
    src        edge_attr  dst
0     0   to the left of    6
1     0   to the left of    4
2     1  to the right of    6
3     4          pulling    6
4     4  to the right of    0
5     4   to the left of    5
6     5               on    6
7     5  to the right of    4
8     6        pulled by    4
9     6  to the right of    0
10    6   to the left of    1