Why do videos go viral on Twitter?

http://blog.twitter.com/2013/how-videos-go-viral-on-twitter-three-stories-0

If you were wondering how and why videos go viral, Twitter has the answer for you — it doesn’t really know. “There are no rules to “virality” — while some ignite, and spread like wildfire across the web, the growth of others is much more measured, like ripples spreading across a lake,” the company wrote in a blog post Monday. Bottom line: after all these years, content popularity on the internet is like playing the lottery — hey, you never know!