Professor Bruce Hood demonstrates how a siamese fighting fish will try and protect its territory when it sees its own reflection. This is because they have no sense of 'self'. Humans on the other hand can read other peoples' body language and gage what they're thinking by being able to have a sense of your own 'self''. 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