The hallux is a backward pointing toe on the foot of a Red-breasted Nuthatch. In humans, the hallux is our big toe. In Red-breasted Nuthatches, it is clearly their biggest toe, but it serves a unique purpose. That toe is what allows these birds to hang off the bark as they scurry down a tree trunk. In this photograph, the Red-breasted Nuthatch is not in its iconic downward facing pose because it is horizontal not vertical. However, the Nuthatch’s big toe is clearly visible especially on its left foot. Apparently, it is unique among birds but natural for this species according to Cameron Ghalambor, a professor of biology at Colorado State University who has studied Red-breasted Nuthatches. I have come to adore the Red-breasted Nuthatch, a delightful little bird, for its iconic stance that seemingly defies gravity as it clamors downhill on a tree trunk. I didn’t realize that the toe that allows it to do this is analogous to our big toe which doesn’t have nearly the flexibility that the Red-breasted Nuthatch has.