Symbolism, Imagery, Allegory
The world's deadliest snake might not be an inspiring image to your average Joe, but for Peekay, who narrowly escapes a brush with the black mamba, the serpent is a reminder of Doc and a sign:
Once I had recovered from my fear, I found the snake an entirely appropriate, perhaps even a magnificent symbol. The black mamba, the most deadly snake in the world, takes one partner for life. If its partner is killed, the second snake will often wait for the killer to return, prepared to die in order to take revenge. Not naturally aggressive, it will nevertheless defend its young, raising itself onto the last few inches of its tail and striking sideways in a whipping action. As most humans instinctively raise their arms in panic to defend their eyes, the mamba fangs most often strike into the top of the upper arm. The journey to the heart is swift and the outcome deadly certain. (23.101)
You'd think this was National Geographic or something by the way he describes the snake. At first, this biological information might seem like just some smarty-pants showing off on Peekay's part. But the end of the novel lets it all come to light. Granpa Chook was Peekay's partner, and all of Peekay's training has been dedicated to getting revenge. And that strike into the upper arm is not casual, either.
When Peekay is in the mines, the snake becomes a warning rather than a threat. The night before he is faced with a running fuse (a fuse that's lit but doesn't look like it), he dreams of the black mamba:
In my dream [...] the fuse turned instead into the black mamba of the crystal cave of Africa: it rose as it had done outside the cave, its head weaving and its darting tongue becoming the spluttering sparks of the lighted fuse. (24.11)
That running fuse is only a false start, because Peekay's biggest challenge is yet to come. During the accident in the mine the rocks skin him as he falls—he's almost like a snake himself with his shedding skins. Finally, he becomes the black mamba as he battles the Judge in their final showdown:
Suddenly the snake was back in my mind's eye, its diamond-shaped head with tiny darting tongue flicking faster than I could blink. (24.84)
Just like the black mamba, which strikes the upper arm of most of its human victims, Peekay, too, takes the Judge down.
Across the jagged blue lines of the swastika the mamba-driven blade cut "PK." Then followed the injection of poison. Smearing my hand into the mass on his shirtfront, I rubbed it into the Union Jack and into the initials to set up a massive infection and cause a keloid to build up on the arm. (24.102)
Just like the black mamba that emerged from Doc's cave, Peekay emerges from the mines. The snake is a great symbol for all of the desire for vengeance burning in Peekay.