This game, unlike the demo, is easy to mod by editing a config.txt file. You can add new graphics, edit the config file, and add as many spawning objects as you want, or even get rid of all the animals and objects and replace them with your own. You can make different sounds play for each animal or object that is hit, different blood thingies to appear when something is hit. I expect individuals such as JEMdev, for example, to release various total conversion mods for the game. I allow anyone to release the EBOOT with their mods as well. I would release the source code but it is nasty looking and the idea of a config.txt file is to change the game without recompiling from the command line every second.
Ideally, you could mod the game from your PSP by using PSPad text editor and yPaint.
The future releases will contain music in the form of .mod, and whatever else I can think of.