I'd like to point out that martyman's suggestions would remove all originality from this game. Shurikens don't come back at you, so they're effectively the same as in any other shooting game. Being able to catch the boomerangs would also defeat the purpose and destroy the mechanic. The idea is that you can only throw boomerangs in one direction so to get the baddies approaching from behind you need to have the boomerang reverse direction and pass by you. It doesn't need to make sense from a real-life perspective. It's a video game, boomerangs don't really move like that, and ninjas aren't real. The difficulty makes the game.