"the worm sometimes turns"

That which has been trodden upon may have its revenge:

CLIFFORD: My gracious liege, this too much lenity

 And harmful pity must be laid aside.

To whom do lions cast their gentle looks?

Not to the beast that would usurp their den.

Whose hand is that the forest bear doth lick?

Not his that spoils her young before her face.

Who 'scapes the lurking serpent's mortal sting?

Not he that sets his foot upon her back.

The smallest worm will turn being trodden on,

And doves will peck in safeguard of their brood.

— Shakespeare's Henry VI, Part III,

The narrator having been put in his place, he now turns on Elliot, referring to the ungentlemanly means by which he acquired his means.