What's the horse pulling?
The horse is pulling a cart.
    src        edge_attr  dst
0     2   to the left of    3
1     3            under    4
2     3  to the right of    2
3     3            below    4
4     4   to the left of    9
5     4            above    3
6     5   to the left of   13
7     9  to the right of    4
8    10        pulled by   13
9    10   to the left of   11
10   11  to the right of   13
11   11  to the right of   10
12   13               on    4
13   13   to the left of   11
14   13  to the right of    5
15   13          pulling   10