As the name suggests this muddy training ground consisted of deep holes which spread along the whole field of 100 yards. Their purpose was to trap the ones that weren't cautious where they were stepping, for most of the wholes were hidden. If you were to fall in one of them, getting out would be a difficult task to accomplish. The purpose of the exercise itself was for the trainees to cross the field without falling in the pits. Memorizing them was out of the question, for their position was changed every month.