We had trouble making the animation work. Here is our attempt.
EDIT: I found the sheet we were given to do this task here: http://nrich.maths.org/6966. There is also a matching interactive resource here: http://nrich.maths.org/content/id/4775/cogs.swf. While it beats ours by miles as it is actually animated, it's not quite what I had in mind. It had a button to add dots on the cogs which is useful for marking. I dotted one tooth on one cog and set the animation going. I then dotted the gap our marked tooth fitted in to and continued. I tried to dot the next gap it fitted in to and that's not possible, only one dot per cog. Shame, it makes it much harder to follow. Much better would be dotted all the gaps it fitted in to, then we could see that either all the gaps had been filled, or that it was cycling through the gaps it had already visited. Even better would be the option to number each gap in the order it is visited, then it is clearer that it's repeating the same gaps in the same order and can't ever escape that pattern to fill the others.
There is also this version (http://nrich.maths.org/810) which has much harder and mathematical wording. The animation is slightly different but has the same limitations.