" 'How can animals be wicked? How can a crab be wicked, for that matter?'
'I don't know, Archchancellor!' Ponder burst out. 'Maybe if they eat forbidden seaweed? Dig a burrow on the wrong day? I'm not a theologian!' "

Archchancellor Ridcully and Ponder Stibbons having a philosophical discussion in "The Science of Discworld III: Darwin's Watch" (from the chapter with the same title as the deviation).

I'm growing increasingly more fond of Ponder. He started out as something of a typical nerd, bright but a bit naïve and socially awkward, at least when it came to explaining things to the other wizards. He used to think everything in the universe could be easily explained if he could only find the key, the right mathematical equation or the right kind of computer, maybe. In the course of the books he's slowly evolved into someone trying to come to terms with the fact that there's more to the universe than they initially expected, and not all of it makes sense even with the right tools. He's less eager to try and explain his complex theories to the senior wizards because he's learned how their minds work. Many times they're on completely different levels, but he doesn't get so worked up about that anymore. He simply does his best to simplify things in a way that gets through even to the other wizards, enough to get them to cooperate when he makes suggestions. He seems more at home at UU than he did in the beginning, which I find interesting.
I like this scene because it perfectly demonstrates that side of his character that still believes the world should be more organised and sensible than it really is, especially Roundworld (= Earth). And he's frustrated when people like Ridcully press him for the answers he doesn't have.

I'm not really happy with this pic, but at least I was able to, for the first time, capture Ridcully like I imagine him, i.e. looking like Sean Connery.