The best thing about this one was, in the middle of the night I failed to notice the special instruction & found the whole puzzle pretty frustrating! Now it's finished I must admit it's quite celever!
The really frustrating thing is I have 4 to go, can only be sure that I have 9 of the 12, and can't see how to get another 3 into the final 4. Aaarrrgghhh! Taking much longer than usual.