What is the truck pulling?
The truck is pulling the machine.
    src        edge_attr  dst
0     0  to the right of   14
1     1               of   12
2     1  to the right of    6
3     1   to the left of    7
4     2  to the right of   14
5     3  to the right of    8
6     3   to the left of    5
7     4  to the right of   11
8     4  to the right of    9
9     4  to the right of   10
10    4  to the right of    7
11    5  to the right of    8
12    5  to the right of    3
13    6   to the left of    1
14    7  to the right of    1
15    7  to the right of   12
16    7   to the left of    4
17    8   to the left of    3
18    8   to the left of    5
19    9          pulling   12
20    9   to the left of    4
21   10   to the left of    4
22   10  to the right of   12
23   11       sitting in    7
24   11   to the left of    4
25   12   to the left of   10
26   12   to the left of    7
27   12        pulled by    9
28   14   to the left of    2
29   14   to the left of    0