Translated from Japanese: Since it’s meat with bones, I stewed it steadily. I want to get collagen.
It was my mistake that the plastic came up after boiling it for a few hours. There was hard, transparent plastic shaped like a sock that seems to have been wrapped around the bones. I thawed the meat, washed it lightly and put it in a pot, but I didn't notice the plastic at all.
I have to be careful next time.