In the book, Artemis is trying to explain a complex plan to his bodyguard, Butler, who is struggling to grasp the nuances. Artemis compares the situation to eating really hot curry, saying:
> "You have to keep your cool, Butler. Imagine you're eating really hot curry. You're not going to understand how spicy it is until you've swallowed it, right?"
Butler, confused, replies:
> "But...how does that relate to catching your drift?"
Artemis, exasperated, says:
> "Exactly! You're not going to understand until you've swallowed it."
The humor of the joke lies in the absurdity of comparing a complex plan to eating spicy food. It's a funny way for Artemis to express his frustration with Butler's slow understanding. The punchline is the fact that Butler is still confused even after the analogy, highlighting the difficulty of explaining intricate concepts to someone who is not familiar with them.