Which kind of animal is the fence behind of?
The fence is behind the horse.
    src        edge_attr  dst
0     0           behind   13
1     0           behind   12
2     1   to the left of   14
3     1   to the left of    6
4     1  to the right of    2
5     2  to the right of    4
6     2   to the left of    1
7     4   to the left of    2
8     5   to the left of   12
9     6  to the right of    1
10    6   to the left of   14
11    8  to the right of    9
12    8  to the right of   12
13    9  to the right of   15
14    9   to the left of    8
15    9  to the right of   10
16   10   to the left of   13
17   10   to the left of    9
18   12      in front of    0
19   12  to the right of   15
20   12   to the left of    8
21   12   to the left of   13
22   12  to the right of    5
23   12      standing in   16
24   12  to the right of   17
25   13      in front of    0
26   13  to the right of   10
27   13      standing in   16
28   13  to the right of   12
29   13  to the right of   15
30   14  to the right of    1
31   14  to the right of    6
32   15   to the left of   12
33   15   to the left of   13
34   15           behind   13
35   15           behind   12
36   15   to the left of    9
37   17   to the left of   12