Hiya myles and fshgk, welcome to MFK. I think the linking of piranhas and snakeheads is just due to the aggressive feeding behavior they show but I am not sure.
yeah man if you want agressive go for snakeheads, piranahs cna be agressive but it will take some work and the right conditiions and even then there not all thaa agressive. plsu if you get like a redline snakehead that could eat a piranha whol enyday when fullgrown. so if you have the tank size get a snakehead.
wow as kool as that would be i would highly sugest against feeding ur snakehead a piranha, I mean even tho ur snakehead could eat the thing whol, piranhas bite franticly when scared and i wouldnt be suprised if the piranah took a nice chunk out of your SH. if i were you i would try a oscar lol.