[Grammar] being economical versus past tense

[Flogger]

Hello

Before getting through my question, I would like to apologize for not knowing the name of such structures in grammar.

The problem is that I don't know when to be economical with English and when to use the past tense. I have intuitionally found that if "and" gets removed after a comma, then English writers want to be economical with their language as follows:

“You can’t get in,” Eleanor said wildly, and again there was a silence, as though the house listened with attention to her words, understanding, cynically agreeing, content to wait.

As you see above, instead of saying ",and understood, and cynically agreed, and was content to wait" the author removed "and" the verbs got changed into an -ing form type (based on my intuition).

However, it seems that the above rule does not apply for the following sentence as I cannot change "spread out" to "spreading out".

Then, from the bottle, a thick bluish smog spiraled to the ceiling, spread out, and gradually assumed the shape of a thick bluish smog with hands, feet, bright-yellow eyes, and a large frowning mouth.

Would you help me figure out when to be economical with language and when to use the -ing form of verb?

 

[emsr2d2]

In the second example, "spread out" refers to a completed action. The smog spiraled and then it spread out. Both of those things have already happened at the time of writing.

In the first example, the understanding, cynically agreeing and being content to wait are ongoing at the time of writing.