Professor Bruce Hood shows an illusion which involves a sculpted face, but instead of the usual convex human face of a sculpture, the sculpture is flipped and we're shown the inside of the face but human brains find it hard to recognise it is convex until the head starts turning around. This clip is part of the Christmas Lectures 2011 presented by Professor Bruce Hood - Lecture Three: Are you thinking what I'm thinking? The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter