Those do look like they could be silverskin. Next time you go to a grocery store, look at like a raw pork tenderloin filet, or a flank steak - they are covered in that stuff. You cannot chew it. The ladies on americas test kitchen say to take a boning knife and slice off as much of it as you can without taking too much meat with it. I am super picky about that stuff, chicken veins, fat, gristle, etc. I am lots of fun at a bbq! Pass me the coleslaw!