The study showed that lack of this gratitude would harm the future of the relationship. Even a false smile was ok.

When participants were asked what the recipient should do they responded:

 “She could’ve done what the entire family does when opening gifts – acted disgustingly gracious and then forget about it,” said one participant.

Roster, C.A. (2006). “Moments of truth in gift exchanges: A critical analysis of communication indicators used to detect gift failure”. Psychology and marketing, 23, 885-903.