Pedantry - Hardcore

The Krogan have a unique physiology in that the have a fully redundant system of nearly every major organ group, twice that of what humans have. They have two hearts, four lungs, four testical (Quads), and even two brains. This redundancy is a large part of what gives Krogan their unique resilience in battle. A rare few Krogan have even more additional redundant organs, such as Quints.