I know - I closed it down at least four times on Saturday evening only to immediately start it back up again and try a different approach (or, rather, mostly the same approach and hope that it would somehow work this time). If I had thought that some of the puzzles up to that stage were difficult, level 20 is the first truly murderous one, and I ended up virtually giving up and looking at a lot of hints to get past it. You can see what it wants you to do, but imagining how on earth to do it is just an insurmountable task.

Then I saw level 21, and it can go and boil its head.