Well...not to encourage the mistreatment of animals or anything but...
You could continue and do it with all the Piranhas. Eventually they will take a liking to human flesh and prefer it over fish/fish food. You then build a pond (inside a secret volcano lair of course!) filled with them. Then just build some type of trap door dropping into the pond and you have somewhere to dump all your enemies.
Then post videos of it (of course!).
This thread is officially back on track.