(Sheep : Beat) , (Horse : Neigh) , (Ass : grunt) , (Owl : Hoot)
Option:
Justification: In all other pairs, second is the sound made by the first.

(Sheep : Beat) , (Horse : Neigh) , (Ass : grunt) , (Owl : Hoot)
Justification: In all other pairs, second is the sound made by the first.