V 着 V 着 就 … 了 (while …-ing, suddenly)

"…and then, mid-action, it just happened"

• Verb + (ongoing -ing)着zhe + Verb + (ongoing -ing)着zhe + then / just就jiù … (completed / change)了le = "while doing X, suddenly Y happened".
• 看着kàn zhe看着kàn zhethen / just就jiùto fall asleep睡着shuì zháo(completed / change)了le = "(I was) watching, and just drifted off to sleep."
• The doubled (ongoing -ing)着zhe sets a drawn-out action; then / just就jiù…(completed / change)了le marks the surprise turn.

V (ongoing -ing)着zhe V (ongoing -ing)着zhe + then / just就jiù + Comment + (completed / change)了le

• Repeat the verb with (ongoing -ing)着zhe, then then / just就jiù + what unexpectedly followed.

he他tātalk说shuō(ing)着zhetalk说shuō(ing)着zhethen就jiùcry哭kū了le。

• variant of 说说shuō(ongoing -ing)着zhevariant of 说说shuō(ongoing -ing)着zhethen / just就jiùto cry哭kū(completed / change)了le = "as he talked, he started crying."

A mid-action surprise

• The pattern shows one action sliding into an unexpected second.

Recap

Read the full reference: HSK 4 grammar — Verb phrases.