다가 그러다

doing that, and then…

"-다가" marks an action broken off or switched out of, and 그러다 stands in for "do that". Together they sketch a sequence without naming it: laughing then getting angry, eating and taking a walk and then an hour has gone by. The other common shape is 다가 그러면, "if you're in the middle of that and then…" — if you have a couple of houses and then that happens, if you hired flexibly and then. It is vague on purpose: 그러다 lets the speaker skip the detail both sides already understand.

Register: casual spoken