Extra points
The penguins on the iceberg can be shot for extra points -- just click them. If you hit them, you will get 5 points. Hit them in the head for 10 points.
Sunk iceberg
During a single player game, you will see an iceberg at the right side of your screen. If you shoot enough, you should find a spot on the iceberg that you can put a hole in. Once this is done, the iceberg will sink.
Shoot the penguins
In single player mode, you can shoot the penguins for 5 or 10 points each. However, in the final round the penguins slide down the iceberg and jump into the air. Shoot the penguins in the air for 50 points each.