How and Why Did This Misinformation Go Viral?

A post claiming that Iran was planning to execute 15,000 protesters went viral. The Prime Minister of Canada condemned the Iranian regime's "barbaric decision" This is misinformation and it has since been deleted but many other viral posts remain. There are a huge range of reasons so we can't be exhaustive. We may not react much differently to 1,000 or 10,000 deaths for one reason: our biased brains.