What was Achilles’ vulnerability according to Greek mythology?

Achilles' vulnerability according to Greek mythology is famously described as his heel. In the myth, when Achilles was an infant, his mother, Thetis, dipped him into the River Styx to make him invulnerable. However, she held him by the heel, which resulted in that part of his body remaining vulnerable. This particular detail has led to the term "Achilles' heel" being used in modern contexts to denote a critical weakness despite overall strength.

The other options, while representing potential vulnerabilities, do not align with the specific and well-known aspect of Achilles' vulnerability. His heart and mind do not represent physical weaknesses in the same way, and his shield is an item of strength, not a point of vulnerability. Therefore, the reference to his heel is both iconic and deeply rooted in the stories of Greek mythology.