Smiling exercise
Step # 1 Ask people to get together in groups of 2. Step # 2 In each 2-person group, ask person A to do this: For the next 7 seconds, no matter what your partner says or does, please show no emotional reaction. Step # 3 In each 2-person group, ask person B to do this: Please look your partner in the eyes and smile.
https://www.linkedin.com/pulse/yes-your-smile-really-contagious-shawn-achor/