There's a mission on the stage A Walk in the Park where you need to go to the top of the level and find Shazza with her car. The mission is knocking out the Blue Tongues by hitting them with boulders, you need to aim your boomerang on the boulders to launch the boulders so they hit the Blue Tongues. The trick is beating patient, wait a bit for the Blue Tongues to approach the boulders, once they're a bit to the right of the boulders, hit them. The game is quite generous with the hitboxes because it's still possible to miss, if you fail, restart the mission and try again.