Butch didn’t shoot Vincent because of the toaster, he would have killed him anyway, because if he didn’t Vincent would have killed Butch. Pulling the trigger straight after the toaster went off was just one of these “cool details” we talk about. After watching the film, you might say to your friends “Hey, remember that part where the toaster goes off and then Bruce Willis shoots that long haired guy and he falls back into the shitter with an ambarassing death pose with a book in his hand, that was cool”
