Do not shoot The Shark Boss at the end of level 4. Instead, shoot the Mini Sharks and let the rocks fall. The ones that fall on left side of the shark seem to glitch and give you points. You can gain a lot of points and some extra lives for the upcoming levels. Be prepared to spend some time here, as it takes awhile to gain each life. Each cycle The Shark Boss repeats will score about 5,000 points. Note: If you do this long enough the level seems to repeat itself. It will revert back to the start but you will still fighting the Boss.