Well Tiercel, if you have never dug to rabbits pal you probably won't see them stuck behind a kill in a stop end that has gone stiff will you?
This is probably where you so called fieldcraft ends, above ground.
The blocking in happens when you have a rabbit with it's arse up, face to the wall of the stop end, the ferret after trying hard gets past to the head end, but is now on the stopend side of the rabbit but making a kill. If this kill stiffens up, in the tube it may take days for the ferret to eat it's way out, thats not if the air supply does not run out, these take some pulling out o