"Zombie shot" is when you're shooting a gun unaware that the safty is on or that you have forgotten to cock the gun, so basicly a dead shot.
Luke: "okay i'm going to aim for the center of the card."
Kevin: "go for it bro."
Luke: -tryes to fire the gun but the tigger is locked- "awh safty's on."
Kevin: "You're a fail."
Luke: 'yeah bloody Zombie shot's."