This "anti-gluttony" doorway, just 32cm (12.6") wide, leads to the kitchen. According to Esquire:
"The monks were required to pass through the door to get their own food from the kitchen and bring it to the refectory to eat. If you couldn't fit, you weren't allowed to eat, which meant you were forced to fast until you lost the weight. Gluttony is a mortal sin, after all."