Fig 1. Overview of the testing arena and the apparatus.

(A) Sketch of the testing arena viewed from the top, including the apparatus and the speakers; (B) Sketch of the apparatus viewed from the side, including the camera, the light, the plastic tube and the trough. In bold topography, a part of the material used for punishments, including the tennis ball relied on a fishing line, the air compressor relied on an air spray gun and a water spray gun; (C) Picture of the apparatus viewed from the front; (D) Picture of the apparatus viewed from the top with a piglet at the trough.