Working quickly, Waterhouse sets two single-edged razor blades into it, the blades dangerously upward-facing, parallel and somewhat less than an inch apart. He holds them in place for a few moments while the frigid metal of the safe sucks the heat out of that glue and makes it hard again. He has employed a pair of toothpicks as spacers to make sure that the blunt backs of the blades do not actually touch the door of the safe; he does not want an electrical connection between them.