Comet triggers and starts resolving at different times (as explained by jako). I cannot think of any other example though.
BTW Comet says “after it resolves” while Tallie Perrault says “when it is trashed after resolving”. Can I play an event (say, Hedge Fund), trigger Comet, gain creds, resolve Comet to play Deja Vu, and get that same Hedge Fund back to hand? Or is it still hanging in the air and didn’t get trashed yet?