Frank Castle: I leave this as a declaration of intent. So no one will be confused. One. Si vis pacum para bellum. Latin. The boot camp Sergeant made us recite it like a prayer. Si vis pacum para bellum. If you want peace, prepare for war. Number two. Frank Castle is dead. He died with his family. Number three. In certain extreme situations, the law is inadequate. In order to shame its inadequacy, it is necessary to act outside the law. To pursue natural justice. This isn't vengeance. Revenge is not a valid motive, it's an emotional response. No. Not vengeance. Punishment.
Candelaria: Vaya Con Dios, Castle. Go with God.
Frank Castle: God's gonna sit this one out.
Frank Castle: Those who do evil to others, the killers, the rapists, psychos, sadists, will come to know me well. Frank Castle is dead. Call me the Punisher.
Harry Heck: You're one dumb son of a bitch. Bringing a knife to a gun fight.
Joan: Say you kill them all. Then what? What makes you any different from them?
Frank Castle: They have something to lose.
Dave: I'm not saying shit!
Quentin: I don't want you to say shit. I want you to answer me.
Answer: In Season 9, Episode 20 of "Mythbusters," Adam and Jamie tested whether a person could survive a "toilet bomb" (recreating a Lethal Weapon 2 scene) by jumping into a cast iron bathtub and being covered with a bomb blanket. They used 1 kg of C-4 explosives that created a blast with a peak lethal pressure of 180 psi outside the tub. The pressure inside the tub was recorded as a survivable 8 psi, though with probable hearing damage. From what I read, a grenade has a much lesser psi force than what the C-4 explosion produced. Depending on the circumstances, it seems plausible that a person could survive the force and shrapnel while inside the tub.
raywest ★