In "Thing Fall Apart" by Chinua Achebe, when does silence occur and what does it mean?

In chapter 7 of Things Fall Apart,
indeed a silence falls upon the Ibo clansmen, for they know they must commit the
unspeakable: kill Ikemefuna.  Achebe describes the event as a kind of
apocolypse:

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the locusts came...a shadow fell on the
world...the sun seemed hidden behind a thick cloud..."Locusts are
descending."

After the
locusts, Okonkwo gets words from Ezeudu that the village has decided to kill Ikemefuna:
"the Oracle of the Hills and Caves has pronounced it."  Ezeudu warns Okonkwo not to take
part.

So, the entire event is shrouded in silence: we never
hear why the villagers want Ikemefuna killed; we never hear the oracle (can one hear
such a thing?); and Okonkwo never tells his son Nwoye or his adopted son Ikemefuna.  The
murder is shrouded in silence to protect the village.

We
may possibly assume Umuofia wants the boy dead because he is reaching manhood, because
he is stronger than Nwoye and therefore a threat to eventually taking a leadership role
in the clan, and because he is an outsider.  So, the communal village must protect
itself against outside threats.

On the day of the
announcement there is an eerie silence on the land:

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The harmattan was in the air and seemed to
distill a hazy feeling of sleep on the world. Okonkwo and the boys worked
in complete
silence...

On
the day of the murder, more silence:

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Okonkwo got ready quickly and the party set out
with Ikemefuna carrying the pot of wine. A deathly silence
descended on Okonkwo's compound. Even the very little children seemed to
know. Throughout that day Nwoye sat in his mother's hut and tears stood in his
eyes...

And, as the men
depart:

At
the beginning of their journey the men of Umuofia talked and laughed about the locusts,
about their women, and about some effeminate men who had refused to come with them. But
as they drew near to the outskirts of Umuofia silence fell upon them
too...

They argued for a short while and
fell into silence again, and the elusive dance rose and
fell with the wind. Somewhere a man was taking one of the titles of his clan, with music
and dancing and a great
feast.

So, everyone knows but
cannot speak: the men, the women, the effeminate men, the children, and especially
Nwoye.  He is angry beyond words.  Okonwko too is angry, but he dare not speak, lest
Ikemfuna cry out.

When the time of the murder comes,
Okonkwo lashes out and kills the boy, despite orders to the contrary, with nary a word.
 In fact, he kills the boy because he broke the silence,
saying "My father they have killed me!"  So, to Okonkwo, words are weak.  They remind
him of his lazy agbala father.  Better to fight to the sounds of
the drum, better to work under the hot sun, better to wrestle in the ring.  Words are
weak.  Silence is manly.