"My Lord-"
"The Elder Wand cannot serve me properly, Severus, because I am not its true master. The Elder Wand belongs to the wizard who killed its last owner. You killed Albus Dumbledore. While you live, Severus, the Elder Wand cannot be truly mine."
"My Lord!" Snape protested, raising his wand.
"It cannot be any other way," said Voldemort. "I must master the wand, Severus. Master the wand, and I master Potter at last."
And Voldemort swiped the air with the Elder Wand. It did nothing to Snape, who for a split second seemed to think he had been reprieved: But then Voldemort's intention became clear. The snake's cage was rolling through the air, and before Snape could do anything more than yell, it had encased him, head and shoulders, and Voldemort spoke in Parseltongue.
"Kill."
There was a terrible scream. Harry saw Snape's face losing the little color it had left; it whitened as his black eyes widened, as the snake's fangs pierced his neck, as he failed to push the enchanted cage off himself, as his knees gave way and he fell to the floor.
"I regret it," said Voldemort coldly.