A case in point would be a scene describing the first appearance of Trimalchio. Here we meet him playing an ancient Roman version of boules (?) with the local dandies and lads about town, his flunkies in attendance.
'Cum has ergo miraremur lautitias, accurrit Menelaus: "Hic est, inquit, apud quem cubitum ponitis, et quidem iam principium cenae videtis. Et iam non loquebatur Menelaus cum Trimalchio digitos concrepuit, ad quod signum matellam spado ludenti subiecit. Exonerata ille vesica aquam poposcit ad manus, digitosque paululum adspersos in capite pueri tersit.' Satyricon 27
‘While we were admiring these displays, Menelaus ran up and said ‘That’s the one with whom you are going to recline at dinner tonight, and what you are looking at now is merely the preliminary to the festivities.’ And he had hardly got these words out when Trimalchio snapped his fingers, at which signal a eunuch ran up and held a piss-pot underneath him. Having emptied his bladder, he impatiently called for a water basin for his hands and having perfunctorily washed them dried his still dripping fingers in the hair of a small boy.'
You need the build-up, the breathless Menelaus excitedly running up (accurit) and pointing the great Man out, ‘Hic est’ ‘That’s him!!’ the ‘iam’ repeated giving a sort of excited flurry to the description. ‘Et iam non loquebatur Menelaus cum...’ Menelaus had hardly uttered this when Trimalchio snapped his fingers…’ (lit: and now/already this was not being said..’ It is interesting to see a verb like loquor –locatus – loqui (Talk, Speak, Utter) in the 3rd person imperfect indicative passive. It suddenly throws the focus on the utterance itself with the image of the words having hardly left Menelaus’ lips – with the immediacy and urgency of a camera suddenly swinging and zooming in. There is an additional aspect; the passive here, I feel, impersonalises Menelaus - he is less important than the words or the utterance and it is Trimalchio (even his Eunuch is ranked above the outside observers as the centre of action) whose actions are active indicative here, ‘digitos concrepuit’ and ‘in capite pueri tersit’
There are many other features like this which make Petronius so lively and vivid but I thought I would post just this one to give you a taste of how the language and the build-up to a lot of these compelling images is just as important, the sum evidently being more than the parts.