The annual scientific festive treat sees Sophie Scott, professor of neuroscience at University College London, talking about language. Aired over three nights, Prof. Scott first looks at how animals use sound to communicate. Tomorrow she looks at silent languages, such as how dogs communicate using smells and how yawning is contagious. In the final episode, Scott talks about what language actually is and how it is changing. Royal Institution Christmas Lectures is on BBC Four at 20.00.