In Harry Potter and the Deathly Hallows, Voldemort thinks that killing Snape will give him full control of the Elder Wand. He uses his snake, Nagini, to kill Snape rather than any number of spells he knows. This allows Snape to live long enough to help Harry defeat him.
Is there any reason that gaining complete control of the Elder Wand would be better facilitated by using Nagini than say Avada Kedavra? Or is this the equivalent of Voldy monologuing?