A boomerang is like karma. What have you put out there that is now coming back to you? Have you put your effort or energy into a project or relationship that is now coming back to you in a positive manner? Or have you put out negativity, harsh words or gossip that is now coming back to bite you?
Perhaps it has not come back yet or you have not put out the effort or energy yet and your dream is reminding you to be mindful of what energy you put out always comes back to you.