Harmen's Dagboek

In this article no in-depth explanation of Chinese characters, hardly references, just an interesting story. There is a fascinating link with hexagram 29 and a passage from the Mozi 墨子. The name of this hexagram, kan 坎, means 'pit, hole in the ground, trap'. But used doubled (kan-kan 坎坎) it is an onomatopoeia for the sound of drumming, as in the poem Fa Tan 伐檀 in The Book of Odes:

坎坎伐檀兮
Kan-kan go his blows on the sandal trees...

Often when a character is doubled it is a representation of a sound. We find this doubling in the third line of hexagram 29:

來之坎坎
The kan-kan of coming/approaching...

Something which produces a kan-kan sound is approaching.

The trigram Water is associated with danger, and with the ears, with listening. All these elements of

• pit
• sound of drumming
• danger
• listening

...can be found in a passage from the Mozi, which describes an alarm system to discover enemies who are approaching a city through underground tunnels. It can be found on p. 799 of Ian Johnston's translation.

Ralph Sawyer describes it like this:

Mo-tzu's counter-methods were premised upon intensively observing the enemy's activities from high lookout towers in order to detect any evidence of excavations, such as new earthen mounts or sudden turbidity in moat or river water. These visual efforts were to be supplemented with a virtual network of listening wells positioned every five paces around the wall's interior, excavated to a minimum depth of fifteen feet or three feet below the water line. Guards, whose task was facilitated by large earthen jars fashioned specifically for the purpose with thin leather membranes stretched over the mouths, were posted at the bottom to carefully listen for any indication of enemy tunneling. Once detected, these multiple wells would allow a fairly accurate determination of the tunnel's location preliminary to mounting countermeasures."
Fire and Water - The Art of Incendiary and Aquatic Warfare in China, p. 33

The drum in a pit, listening for approaching danger - it all fits the imagery of hexagram 29 pretty well. We can even find it in the text of hexagram 29:

Judgment text:
習坎.有孚.維心亨.行有尚.
Repeated kan. Inspire confidence. Protect the inner offering. To proceed is helpful.

The drums are sounding, meaning that enemies are approaching! The lord has to inspire confidence in his people and his army to defend the city. The central offering in the city has to be protected. Proceeding the enemy (as Mozi suggests) is helpful.

Line 1:
習坎.入于坎窞.凶.
Repeated kan enters the pit. Ominous.

The sound that the digging soldiers produce enters the pit through the drums. Danger is coming!

Line 2:
坎有險.(求小得.)
The pit has danger. (Seek small results.)

The sound the drums make signifies danger. (As an oracular omen this means only small results can be achieved.)

Line 3:
來之坎坎.險且枕.入于坎窞.勿用.
The kan-kan of approaching. Danger is more and more nearing. It enters the pit, which is of no use anymore.

The enemies are getting closer, and have reached the drum pits which are close to the city. (see for 'nearing' as a meaning of 枕 the 漢語大詞典, Vol. 4, p. 880). 

Line 4:
樽酒簋貳.用缶.納約自牖.(終無咎.)
Wine vessels and baskets cannot be trusted. Use earthenware. Cover its opening. (In the end no fault.) 

A description of the type of vessel to be used (I translate 納約 as 'to cover' because 納 can mean 'to wear' and  約 'to tie up') and what to do with it.

Line 5:
坎不盈.祇既平.(無咎.)
The kan-drum/pit is not full, the earth spirit is at peace. (No fault.)

The drums do not sound, so nothing is wrong.

I don't see how the sixth line can be linked with all this, and no doubt I am translating the texts in a direction which fits my purpose. Nevertheless I found it a very interesting connection which gives additional meaning & interpretation to hexagram 29 when you receive it as an answer from the Yi.

The Mythbusters have tested the Chinese invasion alarm in one of their episodes.