The scream used in the app is the infamous Wilhelm Scream. http://en.wikipedia.org/wiki/Wilhelm_scream
A note from the developer:
Drop detection is actually much trickier than one would immediately assume. Falling - vertically, not a horizontal toss - must occur, then a collision, and a restful state. Given the raw XZY coordinates from the accelerator data I have been able to create what seems to do the job quite well. If you have issues, please feel free to contact me.
The app is also open sourced, so if you are curious as to how it works, or think you can help, go for it!