The fact that I had trouble spotting a moonwalking bear when it was right in front of the camera speaks volumes about my powers of observation. How long my career as a Sherlock Holmes type of detective would last was already in question even before I watched this clip:

This Transport for London viral is great:

• It's smart, meaning that it'll keep top of mind awareness. Hitting the viewers with a startling realisation of just how unobservant they can be really gets the message across.
• It's tied in closely enough with its desired message (be more observant on the roads) that brand association won't be an issue.
• It's fun enough that people will watch more than once and will send the ad on to their friends.

Now how many differences did you spot? I tallied in with a grand total of one!