Before revision:  Our natural experiment is enabled by the randomness in the mechanism that WeChat, a Chinese online social networking platform, uses to split an online monetary gift (also known as a "red packet") to its recipients. Our results show that recipients on average pay forward 10.34 \% of the amount they receive.
After revision:  Our natural experiment is enabled by the randomness in the mechanism that WeChat, a Chinese online social networking platform, uses to split an online monetary gift (also known as a "red packet") in WeChat groups is randomly split between group members, we are able to conduct a natural experiment to identify the causal effect of receiving online red packets on the contagion of gift exchange. Analyzing gifting behavior using a large-scale dataset of 3.4 million WeChat users, we find that recipients on average pay forward 10.34 \% of the amount they receive.