"We ended up having to establish all of his wounds way earlier than anticipated because Millie [Bobby Brown] broke her knee while we were on our first hiatus. I got a call during the hiatus giving me a heads up about doing the post-sauna scene with Billy on the stairwell getting his wounds nursed the day after we were to get back from hiatus. I hadn't even seen a preview for the sauna fight, so I didn't know how he was getting hurt or where his wounds might be. I just had to have a bunch of stuff made and hope that it would work. I had 50 different kinds of prosthetic pieces made and we had to rush-order all of them from Robert Kurtzman MUFX , who made them for us very quickly.