Do you see a sandwich or a knife?
No, there are no knives or sandwiches.
   src        edge_attr  dst
0    1   to the left of    6
1    1  to the right of    2
2    2   to the left of    1
3    3  to the right of    6
4    3   to the left of    4
5    4  to the right of    3
6    6   to the left of    3
7    6  to the right of    1