Explain what Simon does at night that is a bit out of the ordinary in Chapter 5 of Lord of the Flies.

In William Golding's allegory, Lord of the
Flies, Simon is the most symbolic of characters, and this symbolism is
evident in Chapter Five.  Jack attempts

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..."to talk about this fear and decide and
decide there's nothing in it.  I'm frightened myself, sometimes; only that's nonsense! 
Like bogies.  Then, when we've decided, we can start again and be careful about things
like the fire."

He wants to
give the problem a definitive answer that will satisfy the boys and quiet their
anxities.  However, the intuitive Simon knows that this anxiety cannot be given a name. 
In this pivotal chapter, Simon withdraws from this useless conversation in which Jack
summarily declares, "there is no beast in the forest," and does what no one else would
dare:  He goes "out in the darkness."  When Simon returns, even Ralph questions him with
astonishment, "What were you mucking about in the dark
for?"

Like the prophet that he is, Simon tries to explain
"the place I know,"--his retreat in the forest where he can quietly listen to his
intuitive spirit--but Jack ridicules him.  Little Percival, whose ancient name suggests
man's atavistic need to give troubling elements a name is placed in front of the group
and says that the beast is in the sea, Simon, the prophet, grabs the conch and makes
efforts to tell the boys the truth he has discovered. 
However,

Simon
became inarticulate in his effort to express mankind's essential illness. Inspiration
came to him.

But, Jack
reduces his effort to ridicule again, and Simon's
effort

fell
about him in ruins; the laughter beat him cruelly and he shrank away defenseless to his
seat.

Also symbolically,
Ralph "peered into the gloom."  When he tries to understand, he cannot, just as so many
cannot intuitively understand as does Simon that the evil is not in the forest, but is
within them and is emerging as the vestiges of civilization are cast off by Jack and the
hunters.  This pivotal moment of Chapter Five is expressed in Golding's concluding
paragraph:

A
thin wail out of the darkness chilled them and set them grabbing for each other. Then
the wail rose, remote and unearthly, and turned to an inarticulate gibbering.  Percival
Wemys Madison, of the Vicarage, harcourt St. Anthony [civilization] lying in the long
grass, was living through circumstances in which the incantation of his address was
powerless to help him.