Einstein Hollow Face optical illusion Mask (party trick/statement piece)

I first read about this in Dawkin's God Delusion, then it was featured in QI! that was this exact version! I've had a look online and saw a few different versions of hollow face illusion. none are this good (e.g. there's a smaller Einstein one in usa, and on the wiki page there's a really poor Bjorn Borg one).

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