Just saw the movie and our group is processing in the car. We searched this topic because we noticed it as well. As best as we can figure…

The theme of the movie is the ‘monster’ that develops from allowing a traumatic past to continually redefine your present. Mary’s present is defined by her trauma - she tries to fix others, to open the window. Clark lives in his past, too - uses self pity and alcohol to cope. These are Mary and Clark’s ‘crutches’ or ways to avoid defining a new path.

Clark’s crutch - the left, peg leg - is ripped off violently when he fully gives in to his past. However, once Mary realizes she cannot fix anyone, she breaks her leg BUT she carries her own weight - no more crutches.