My left arm extends all the way up to and just barely past my elbow, tapering into a small, fleshy stump. For prosthetists, I've always been a weird fit--that funny little kid in the office with my arm held out like a bird with a broken wing, waiting for the plaster mold to dry. Since I do not have a forearm, a prosthesis socket must fit over my elbow to stay on, but the socket necessarily limits the range of motion and makes it harder to prevent falling off during a full day of bending and extending. My most recent prosthetist had devised their own patented method of molding a socket that better accommodates bodies like mine. What I didn't realize was how else they have applied this knowledge, before I even became their patient.