In Great Expectations, what are the unusual experiences that Pip had on Miss Havisham's birthday?

It is Chapter Eleven of this memorable novel wherein Pip
is summoned to visit Miss Havisham on her birthday. The whole chapter is very strange,
especially the setting and the action that occurs. As Pip goes to Miss Havisham, she
leads him into another terribly decayed room:

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The most prominent object was a long table with
a tablecloth spread on it, as if a feast had been in preparation when the house
and the clocks all stopped together. An epergne or centre-piece of some kind was in the
middle of this cloth; it was so heavily overhung with cobwebs that its form was quite
indistinguishable; and, as I looked along the yellow expanse out of which I remember its
seeming to grow, like a black fungus, I saw speckled-legged spiders with blotchy bodies
running home to it, and running out from it, as if some circumstances of the greatest
public importance had just transpired in the spider
community.

It transpires that
this is Miss Havisham's wedding cake that has been allowed to rot and decay. As Pip
walks with Miss Havisham, her relatives try to make conversation with her and are cut
off. Miss Havisham says that they will all see her laid out on this table at her death,
and it is clear that most of the guests are there because they hope to gain something
when she dies.

As Pip leaves, he meets a strange pale young
boy with whom he fights. The fight is described in hilarious terms, with the stranger
pretending he knows all about fighting but in fact shows himself to be
incompetent.