thou shalt go to holyfell and get into the loft that is over the outer door , and pull up the boards of the floor , so that thou mayst thrust a bill therethrough ; then when snorri goes out to his privy , thou shalt thrust the bill through the floor of the loft into his back so hard that it may come out at his belly ; and then leap off out on to the roof and so over the wall , and let the mirk night cover thee .