The article explores how different animals in a food chain have varying magnesium isotope ratios in their bones. By using a new method, researchers found that herbivores, omnivores, and carnivores show different patterns of magnesium isotope fractionation. The results suggest that two processes are at play during bone formation: one related to equilibrium and another to kinetic fractionation. This new approach can be applied to study stable isotopes in other elements with multiple isotopes.