How does Terry Pratchett use imagery in Guards! Guards!?

Imagery:

"By the small portable sacrificial altar a tethered billy goat was peacefully chewing the cud and possibly thinking, in Goat: What a lucky billy goat I am, to be given such a good view of the proceedings."

"Vimes was vaguely aware of a brilliant blue dress that sparkled in the candlelight, a mass of hair the color of chestnuts, a slightly anxious face that suggested that a whole battalion of skilled painters and decorators had only just dismantled their scaffolding and gone home, and a faint creaking that said underneath it all mere corsetry was being subjected to the kind of tensions more usually found in the hearts of large stars."