During her first night in the cell, Nell discovered two other things. 
First, the latch on the little door through which her food was delivered was 
partly accessible from her side, and with a little effort she was able to jam 
it so that it no longer locked properly. After that, she was able to stick her 
head out of the hatch and examine her surroundings, including the mechanical 
lock. Or she could reach out with one arm and feel the lock, spin the crank, 
and so on.