"If they tell you how much they loved your gift and if the smile is missing the contraction of the sphincter muscle around the eye -- the crow's-feet wrinkles -- the person probably wasn't so keen on your gift," said Cohn.
Cohn uses a method called Facial Action Coding System [FACS] developed by famous researcher Paul Ekman to train students to detect such signals. But Cohn warned it isn't something that can be picked up in a day.
"It is something that can be learned," said Cohn. "When we train people in the lab, typically it would take a semester."