In the context of the passage you provided, "hint" and "curve" are used to describe physical characteristics of the body. "Hint" in this context suggests that there was a slight indication or suggestion of curves (typically associated with body contours or shape) previously, but it was not very pronounced or visible. The mention of "a layer of fat used to hint at curves to come" means that there was some fat on the side of the body that gave a subtle suggestion of future curves, perhaps as the person lost weight or developed more muscle, which would enhance their body's natural contours. "Curve" refers to the natural curves or contours of the body, such as those in the waist or hips. In this context, the word is used to describe the expected or desired changes in body shape that are becoming more noticeable now that the person is seeing muscles in their arms, legs, and stomach and pinching the side where the fat used to be. So, essentially, the passage describes a change in the person's body where they are noticing more defined muscles and a reduction in fat, which is revealing the natural curves and contours of their body that were previously hinted at by the presence of a small amount of fat.