Five just for having something fairly original. If you want to add onto the idea I'd suggest making the soundwave effects look like ripples in the water when they hit stuff for a cooler look, automatically emit sound, a different perspective with the ground on the bottom of the screen and the sky on top, and moving enemies/bugs(food).
Nice art too.

A very good and funny game.

Here are some of my thoughts:
- my screen is a laptop screen and I cannot see the entire screen (even in full mode), the objects/bat do not need to be so big IMO;
- the background graphics/story are appealing (though some are hard to understand), but the graphics of the game itself are much simpler and not very appealing;
- when I clicked on instructions and saw no back button I had to refresh the entire page in order to restart the flash, since even pressing ESC, ENTER or any other key does not work in that section;
- the bat should only perceive his surroundings when the waves that touch the objects hit him back;
- microbats eat insects, fish, rodents or drink blood and echo-locate;
- megabats, sometimes called flying foxes (due to their size and similarity), are herbivores and eat fruits, nectar or pollen and DO NOT echo-locate (they aren't nocturnal creatures, just found this in wikipedia);
- I did not realize I got any extra points when the bat touched the fruit, it would be easier to understand it if a sound or a visual clue was produced when that happened;
- why do we need to press ENTER to start the game and then use the mouse to select an option from the menu when the game itself does not make use of the mouse?

Overall, the story drawings are appealing and I believe the concept of having a bat flying around with eco-location fetching things is interesting.
However, since eco-location-bats do not eat fruits and the limitations that the game impose are so strict (touching anything except fruits ends the game) I stopped playing after my second attempt. If these "fruits" were, for example, live animals that moved around and the bat would have to stop to eat them and a snake could come to eat the bat, that would make more sense.