Movement amongst the trees of a forest shows that the enemy is
advancing.
Ts‘ao Kung explains this as “felling trees to clear a passage,”
and Chang Yü says: “Every army sends out scouts to climb high
places and observe the enemy. If a scout sees that the trees of a
forest are moving and shaking, he may know that they are being cut
down to clear a passage for the enemy’s march.”
The appearance of a number of screens in the midst of thick grass
means that the enemy wants to make us suspicious.
Whenever the meaning of a passage happens to be somewhat elusive,
Capt. Calthrop seems to consider himself justified in giving free
rein to the imagination. Thus, though his text is here identical
with ours, he renders the above: “Broken branches and trodden
grass, as of the passing of a large host, must be regarded with
suspicion.” Tu Yu’s explanation, borrowed from Ts‘ao Kung, is as
follows: “The presence of a number of screens or sheds in the
midst of thick vegetation is a sure sign that the enemy has fled
and, fearing pursuit, has constructed these hiding-places in order
to make us suspect an ambush.” It appears that these “screens”
were hastily knotted together out of any long grass which the
retreating enemy happened to come across.