Did he use an animated GIF ?
You could use an animated gif for this challenge but your limited to 256 colours which is a real pain.

I am going to try a webm format video which is supported in quite a lot of browsers now - but I dont expect the forum to support it... Aaaand no, the forum doesnt even tho my browser does !

So basically it comes down to this. Either you supply a file which is an animated GIF with limited colours, or you use an APNG one with great colours only limited browser support or you supply a link for a video file like WebM which is hosted on another site. Not a great choice that eh ?