I have three cats and only one of them will eat those stringy bits in the FF. I tried mashing it up with a fork, and that goes ok with two of them.
I have decided to feed them mostly dry food, and fresh cooked meat once in awhile. One cat likes only chicken and beef, the other two like fish.
I always suspect what might be in cat food in cans. I mean: what else can they put in there? When you think about it, it could be most anything... remember Gilda Radner's bit on hot dogs and toenails?...."It's nadda toenail, but it looks like a toenail...."