An attack by what caused The Banker to go mad

[macpark]

I need help to answer this quiz question:

An attack by what made The Banker go mad.

[eah]

number of letters ? any given letters?

bonkers?[not you]!

[macpark]

Not a crossword eah!

Just a quiz in the book category

[Huderon]

A Bandersnatch.

The Banker is one of the crew in The Hunting of the Snark by Lewis Carrol. In Fit The Seventh he rushes ahead of the rest of the crew and is attacked by a Bandersnatch withe the result that :

He was black in the face, and they scarcely could trace
The least likeness to what he had been:
While so great was his fright that his waistcoat turned white-
A wonderful thing to be seen!

To the horror of all who were present that day.
He uprose in full evening dress,
And with senseless grimaces endeavored to say
What his tongue could no longer express.

Down he sank in a chair--ran his hands through his hair--
And chanted in mimsiest tones
Words whose utter inanity proved his insanity,
While he rattled a couple of bones.

[Whickerman]

Three stars warranted there, surely!