When Fear Looks Like Surprise

Recognizing emotions from other people's faces is one of the most important social skills we possess. Yet, we do not always get it right. Have you ever looked at a human face and wondered whether the person was terrified or simply surprised? This is one of the most common emotional confusions. But why does it happen?
To answer this question, in a recent study we investigated what happens when people express these emotions spontaneously versus when they intentionally recreate them (for example, when posing for a photograph). Using a three-dimensional technology that captures facial movements with extreme precision, we measured in detail how different facial muscles move during emotional expressions.
The main finding was striking: fear is confused with surprise much more often when the expression is posed. The reason lies in the dynamics of facial movement. When people produce these emotions in a non-genuine way, their facial muscles move in almost identical patterns, creating a substantial kinematic overlap.
Spontaneity, however, does not lie. In genuine emotional expressions, clear differences emerge. Authentic fear, for instance, is characterized by much larger and faster mouth movements than surprise.
These findings suggest that our brains are tuned to detect the dynamic nuances of real emotions, which contain unique and informative movement patterns. Relying solely on stereotypical or laboratory-based expressions (such as photographs of faces) may provide only a partial picture of how we interpret others' emotions. The next time you are unsure whether someone is afraid or surprised, pay attention to the speed of their facial movements: genuine spontaneity leaves a signature that is difficult to imitate.

Reference: Scarpazza, C., Straulino, E., Sartori, L., & Del Popolo Cristaldi, F. (2026). Preliminary evidence of kinematic overlap in posed, but not spontaneous, facial expressions of fear and surprise. Scientific Reports. https://www.nature.com/articles/s41598-026-47026-3