Basically an unholy DK's are a bit buggy right now, the ghoul stun (gnaw) looks like it's on cool down but if you click it it will still activate, me and a friend were testing it and were able to get a double stun off or more each time. Basically, just use gnaw then click it again it looks like it's on CD but will allow you to cast again.
EDIT Works for leap also, the ghoul has to have below 30 energy when this happens just spam the ability. So, spam claw till low energy then use stun/leap