onactivate>self>vce_something>onplayerlastmessage = boomonvariabletrue>self>spawnprojectile>rocketThat's roughly how it should look. The only thing I may have gotten wrong is the event names.
Noedit: Forgot one thing, you should make the loop start brick toggle off when you first click it, and toggle back on when you hit the "player has said boom".
Dude sorry I can not read the form of events you are stating. Can you make it a little easier?