What and Why is Collier uncovered during "The Will of Stanley Brooke"?

Question

The Will of Stanley Brooke is a Cthulhu Mythos short story by Ramsey Campbell. In it:

Stanley Brooke dies. Then an identical man called William Collier mysteriously appears, his movements clumsy and his skin pallid and waxy. Relatives then discover that the dead man has left his estate to this bizarre simulacrum in the will.

The rest of this question contains spoilers for both that story and H.P. Lovecraft's The Festival which I won't hide, as it would render the whole question blank. You have been warned.

Late in the story Brooke's lawyer, Mr Bond, suddenly realises something is amiss. Brooke's relatives are trying to claim a portion of the will for their own, and the impostor replies:

'Oh please don't try to be subtle,' Collier advised her. 'I know what you're after, and I can tell you now that I wouldn't dream of splashing my money about.'
'Why, you worm-' begin Emily.
Collier recoiled and collided with a sideboard, overturning a vase.
'My God,' Bond said tonelessly.

This the moment Bond realises there's something very wrong with Collier and he forms a plan to take action.

However, I have never understood what it was that causes Bond to make the sudden realisation. Nothing in particular happens to change things or provide new information, and up until this point, Bond seems happy to accept Collier as he is. What changed?

Furthermore I had always assumed that the connection between Brooke and Collier was deliberately hidden to heighten the horror of the tale. Is he undead, or something worse? However, in his introduction to the short story collection Cold Print, Ramsey compares this story with The Festival by H.P. Lovecraft. This features an old man wearing a lifelike wax mask to disguise something far worse underneath. Is there anything in The Will of Stanley Brooke which suggests Collier is somehow disguised?

Answer 1

I think the clue does indeed have to do with the word "worm," as mentioned in another answer. Bond recognizes that William Collier is some sort of worm-related entity.

As literary forshadowing, the word "worm" is prominently used to describe Stanley Brooke on other occasions:

'The worm!' Emily said. 'After all I did for him, and what my daughter did too—'

_{"The Will of Stanley Brooke"}

More specifically, however, I think this alludes to a phenomenon mentioned in the Lovecraft short story "The Festival":

For it is of old rumour that the soul of the devil-bought hastes not from his charnel clay, but fats and instructs the very worm that gnaws; till out of corruption horrid life springs, and the dull scavengers of earth wax crafty to vex it and swell monstrous to plague it. Great holes secretly are digged where earth's pores ought to suffice, and things have learnt to walk that ought to crawl.

_{"The Festival"}

As noted in the question, the author references the connection with "The Festival."

While interpretations of this passage vary, and some people believe it refers to a worm-infested walking corpse, I've always thought it to refer to one very large worm that can disguise itself as human ( "swell monstrous to plague it"). However, in "The Will of Stanley Brooke," it might more likely be worms puppeting his corpse, since it's several small worms, seemingly, that we see at the end.

Notice also the title allusion: it is the disembodied will of Stanley Brooke ("the soul of the devil-bought") that impels this horror.

Also, consider this passage, that makes Collier drop his spoon:

'Well, you know... if you eat too much pork you'll get like a pig, and I suppose you'll get pretty fishy if you eat nothing but fish... In fact, if you concentrate on one food, I think pretty soon you'll look exactly like it.'

_{"The Will of Stanley Brooke"}

The worms that ate his corpse "look exactly like" him!

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As a side note, I've always found this story a bit strange. In "The Festival," the worm-things are clearly antithetical to humans. They're instructed by the spirits of the "devil-bought," "vex" the Earth, and so forth. They also engage in all sorts of disquieting rituals. However, in this story Collier seems sociable and decent, and Bond nonetheless (re)kills him.

Answer 2

I'm not sure either but it has something to do with his reaction to the word "worm", and later Bond is chopping up something that's buried in his garden that is described as pale and writhing that he says are "worms". It's uncertain what the creature actually was, though.