How tall is the fence?
The fence is short.
    src        edge_attr  dst
0     0   to the left of   21
1     0   to the left of   15
2     0   to the left of    6
3     0   to the left of   11
4     0   to the left of    9
..  ...              ...  ...
71   21  to the right of   15
72   21  to the right of   18
73   21  to the right of   12
74   21  to the right of   13
75   21  to the right of   20

[76 rows x 3 columns]