Not sure if anyone watched this movie closely enough to know, but..

What exactly is that brace-like thing on Franz's hand?
is it a prosthetic hand, or what?

in any case, I'd like to thank that weird thingy for being the reason for his trademark "what-did-you-say?-punch!" :D

it's a true shame we didn't get to see more of Franz in the film.
Oliver Korittke did a hell of a job with his supporting role!