Why YouTube video goes viral

According to Allocca at TED Talk, there are three factors:
1. Tastemaker - video unnoticed when first in YouTube, but got noticed
when the video tweeted by popular tweeter.
2. Unexpectedness - Something unexpected happens which makes the video
funny. Eg the bicycle crash into a lamppost during the host speaking
something on the bike.
3. Participation - eg second creation on the original video. Eg.
Flying cat video
Check out this amazing TED Talk:
Kevin Allocca: Why videos go viral
http://www.ted.com/talks/kevin_allocca_why_videos_go_viral.html