It makes intuitive sense that you need a sharp tool to puncture through a tough material. The typical approach to evaluating sharpness in biological puncturing tools is to treat morphological measurements as a proxy for puncture ability. However there are multiple approaches to measuring sharpness, and the relative influence of morphology on function remains unclear. Our goal is to determine what aspects of tip morphology have the greatest impact on puncture ability, using a) viper fangs and b) engineered punches to isolate the effects of different sharpness measures. Our results indicate that tip included angle is the strongest predictor of puncture performance in both viper fangs and engineered punches. For puncture tools with small included angles, sharpness index (based on radius of curvature) also affects puncture ability. Finally, we found that punches serve as good predictors of fang performance at small angles and sharpness index values.