Those of you with kids, or with a foot in the toy design world, are probably familiar with Magformers. If you're not, scan through the vid below to see some examples of this modular educational building toy in action:
The brilliance of the Magformers system is that the magnets always rotate to form attractions, rather than repelling each other. This makes for a satisfying, hassle-free play experience for your child, who can easily join the shapes together.
It's therefore funny to see Matthias Wandel show you how to render the magnets uncooperative, so that "if you've got a kid that's really anal retentive," you can drive them nuts: