Making Underground Passages
The crew developed tools for chiseling through concrete alongside the inflatable device and dummy heads. The instruments were rudimentary, but they did the job. They did this by robbing the kitchen and the woodshop. Every night, they spent about 3.5 hours chipping away at the concrete surrounding their cell after (quietly) removing the bolts from the vents. It must have been a prolonged process. In time, however, they carved out entrances large enough for humans to squirm through.