A small brown bear walks directly toward the viewer along the rugged, rocky coastline. It navigates the shoreline with purpose, seemingly undeterred by the steep rocks and photographer nearby. Fortunately, I was on a boat with a long lens, so I was not too worried. Generally, one cannot determine whether a brown bear is small or large without some external reference for scale. A single bear, viewed in isolation, provides no reliable size cues because fur length, posture, perspective, and camera angle can make the same animal appear much larger or smaller. Humans infer size by comparing the bear to known objects (trees, rocks, people), by seeing multiple bears together, or by observing movement and proportions over time. Without any feature for scale, size judgments are essentially guesses rather than measurements. Photographer: Sean Neilson