ressasser

Il faut ressasser la farine.

You have to sieve the flour again.

J'étais dans ma chambre, en train de ressasser l'opportunité manquée.

I was in my room, brooding over the missed opportunity.

Si tu continues à ressasser ses défauts, il va finir par t'en vouloir.

If you keep harping on his flaws, he'll grow to resent you.