For grain free diets: they supplement grains with lentils, peas, and white potatoes which is high in Lectins. Lectins block the heart from producing taurine, a heart regulator. Without taurine, their heart dilates (cardiomyopathy) and they die. They naturally produce it, but the lectin foods block that. So by adding prey heart (turkey heart, chicken heart, etc) it can supplement the taurine that they need. Or just don't feed grain free 😂