In this ‘uncut’ special episode, recorded before an audience at the Hay Festival in Wales, Chris and Xand discuss the anatomy of the smile, explore its evolutionary origins and examine some of the health claims about the power of the smile.

Can a smile really give your brain the same reward as two thousand bars of chocolate? Will putting a pencil in your mouth make you feel happy? And how do you fake the perfect smile when realising you’ve failed to win a BAFTA for the eighth time?! Expect some science and some silliness and a dog that looks like a loaf of bread.

Featuring Professor Ben Garrod from the University of East Anglia, Dr Magdalegna Rychlowska from Queen’s University, Belfast, Sinead Rushe from the Royal Academy of Dramatic Arts in London and jack the African street dog.

If you want to get in touch, you can email us at whatsupdocs@bbc.co.uk or WhatsApp us on 08000 665 123.

Presenters: Drs Chris and Xand van Tulleken Guest: Professor Ben Garrod, Dr Magdalegna Rychlowska, Sinead Rushe Producer: Rami Tzabar Executive Producer: Jo Rowntree Editor: Kirsten Lass Assistant Producers: Maia Miller-Lewis and Grace Revil Tech Lead: Reuben Huxtable Social Media: Leon Gower Digital Lead: Richard Berry Composer: Phoebe McFarlane Sound Design: Melvin Rickarby

At the BBC: Assistant Commissioner: Greg Smith Commissioning Editor: Rhian Roberts

A Loftus Media production for BBC Radio 4.