Kip
Idea missing.
It looks like there's conflicting evidence. The Wiki (thank goodness for that lol) says there's a point where Hermione silences someone, who proceeds to hit her with a spell that someone later says could have killed her if he had his voice for the incantation. Then, on the other hand, there seems to be plenty of instances where the Killing Curse works nonverbally, and if that one works, seems like all the rest should too.