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Toys that let children draw by moving a magnetic pen over a tablet filled
with magnetic particles can leak if they puncture the top surface. So Takara of
Japan has invented a tablet that traps a suspension of magnetic particles in a
honeycomb of tiny cells moulded from resin, each with a clear top (GB 2345270).
The honeycomb is topped with a transparent protective layer. Even if a child
stabs the top surface with pen, just one or two cells will be punctured,
releasing only a very small quantity of fluid.