This week, Mike Williams asks why do we shake hands? All over the world millions of us use this gesture to greet others but where does this everyday ritual come from, and what purpose does it serve? With the US presidential election just days away, Mike also looks at the role of the handshake in political life - why has it proved to be such a sensitive issue?(Image: US President Barack Obama (R) and Republican presidential candidate Mitt Romney (L) shaking hands. Credit: TIMOTHY A. CLARY/AFP/Getty Images)