The piranha tank is an apparatus designed for carrying out executions. The device consists of a foot pedal trigger and a collapsible bridge suspended over a tank containing predatory fish. The equipment was featured in EON Productions' 1965 James Bond film You Only Live Twice.
Blofeld's Piranhas are predatory fish that Blofeld keeps in a pool in his Volcano Lair. He uses them as a method of execution for those who displease him, such as Helga. They can reportedly strip a man to the bone in minutes. Bond later knocks Blofeld's bodyguard Hans into the pool and jokes "Bon Appetit" to the Piranhas.