Though his fingers move, the prosthetic remains unchanged. Lune knows what she's expecting it to change to: a limp and broken shape. Fitting to remember it that way. After all, the arm was Gustave, when they memorialized him.

"You'd better be one of those working parts."

She lifts an eyebrow at him. Trying to come at it in a way he might appreciate. Better to take a working Gustave with his gun in one hand than a two-handed Gustave who might freeze in the heat of the moment.