If birds gather on any spot, it is unoccupied.
A useful fact to bear in mind when, for instance, as Ch‘ên Hao
says, the enemy has secretly abandoned his camp.
Clamour by night betokens nervousness.
Owing to false alarms; or, as Tu Mu explains it: 恐懼不安故夜呼以
自壯也 “Fear makes men restless; so they fall to shouting at night
in order to keep up their courage.” The _T‘ung Tien_ inserts 喧
before 呼.