How the hell do you know the power of the bite of a piranha. Are you a piranha expert?

What's so hard to believe besides your contention that a piranha can't "easily" bite off a person's finger.

I found a place that sells pirnhas for $28 plus shipping.
Anybody (if they will ship to you that is) can get a piranha relatively cheap and release it in a public place to reek havoc.

http://www.riverwonders.com/catalog/i31.html