The experiments were carried out in an experimental box made of black polyvinyl chloride boards. In this box, there
were three areas (pool, ground, and food: Fig. 1b). In Experiment 2,we used the two of the three areas,the ground and
food areas,but there was no food in the area.There was a hole in the partition 85 mm in diameter between the two areas.
The hole of the other side in the ground area was covered.