Is It Logical...?
In "Sarek" from "Star Trek: The Next Generation," Sarek is suffering from Bendii Syndrome, the Vulcan equivalent of Alzheimer's. Picard has the unenviable task of confronting him with this. When Sarek tries to refute his claims of being emotionally affected, Picard points out that Sarek was crying at the ship's concert, that he saw the tears. Sarek tries to rationalize this away as there having been only one tear, but Picard has a simple question which cuts to the heart of the matter: "Is it logical for a Vulcan to cry?"