Not all viral videos were created (or perform) equal. Most seemingly-instant-classics cause a huge, abrupt spike in interest from people searching around the world, only to just as quickly disappear until it's time to create those year-end top 10 lists.

Take, for example, Ted Williams, the homeless man who became an international star after his incredible voice was discovered on a Columbus roadside. Various versions of that video were viewed tens of millions of times in early January. Below is a graph of relative searches for "golden voice" during that month:



So now let's compare that to March's biggest viral star, Rebecca Black. Interest in the singer has persisted well beyond the first few days of that trend. She's still a trending topic on YouTube today, nearly a month later. Why?

Initial theories:

1. It's a song. In general, music videos often behave differently than other types of popular videos because they naturally stand up better to repeated viewings. In a case like this, the song gets stuck in your head, so you might decide to listen to it again.
   
   
2. It's more ripe for parody. Even now, we are still seeing large numbers of Rebecca Black parody and cover videos appearing all over the site. (A search will turn up over 1,000 Rebecca Black parodies from just this week.) Today, a religious version is trending and, earlier this week, we even discovered one from Brazil in Portuguese.

But there's one clear, additional factor that separates Rebecca Black's "hit" music video from all others and it's depicted in the chart below, which tracks relative search interest gobally in "Rebecca Black" over the past 30 days or so:



"Rebecca Black" searches see a jump every Friday.

(The weekly spikes are even more pronounced for the word "Friday," which is a term that's seeing more searches now than it ever has on YouTube.)

The video, which has been seen approximately 90 million times, will likely have another bump today as our data shows that -- just like searches for the song -- views of the video also increase every Friday. Interesting aside: even though "Friday" blew up the week of the 13th, the single day that the video was watched the most times was Friday the 25th, well after the song had become completely ubiquitous, which underscores the fact that the way we watch this video differs from others.

This whole day-appropriate-video-watching phenomenon is nothing new. As we documented back in February, video views for the 1995 Bone Thugs-n-Harmony jam "First of the Month" still increase sharply every first day of each month.