What is in those Delectable treats that is so addicting?

Meet Seamus.

I don't understand what is in those Hartz (I know) Delectables Bisque treats that make my cat crazy. At first I thought it might be the tuna, but I tried just the chicken recipe and he still scarfs them down. They are just so expensive. I tried pureeing a can of Fancy Feast Kitten Ocean Whitefish pate because I have about 15 cans left over from his tiny kitten days. Turned his nose up at it. I even warmed it in the microwave for a few seconds. All the package says is water, chicken, natural flavor, tapioca starch, guar gum, annatto extract color, carmine color. Obviously, the tuna ones have tuna instead of chicken. What could possibly be in there? Anyone have success with some other substitute? I know there are other brands but those are even more expensive. Thanks.