The carts are carrying what?
The carts are carrying luggage.
    src        edge_attr  dst
0     1   to the left of    7
1     2   to the left of    6
2     3   to the left of    9
3     6  to the right of    2
4     7  to the right of    1
5     7   to the left of   12
6     9  to the right of    3
7    11         carrying    9
8    11  to the right of   13
9    12  to the right of    7
10   13   to the left of   11