Are the pens on the right side or on the left?
The pens are on the right of the image.
    src        edge_attr  dst
0     2   to the left of   11
1     2  to the right of    5
2     2               of    8
3     3  to the right of   13
4     3               on   15
5     4   to the left of   12
6     5   to the left of    2
7     5   to the left of    8
8     5   to the left of   10
9     5   to the left of    9
10    5   to the left of   13
11    5   to the left of   12
12    6   to the left of   12
13    7   to the left of   12
14    8  to the right of    5
15    9               of    8
16    9  to the right of    5
17   10  to the right of    5
18   11               of    8
19   11  to the right of    2
20   12  to the right of    6
21   12  to the right of    5
22   12  to the right of    7
23   12  to the right of    4
24   13   to the left of   15
25   13  to the right of    5
26   13   to the left of    3
27   15  to the right of   13