Bald caps, sparrow raps and lightning claps

If you were lucky enough to be at rapper Pitbull's recent concert in Hyde Park in London, you would have been greeted by a sea of bald caps. A Guiness World record-breaking sea of 22,141 bald caps. And, in honour of this incredible feat, the Unexpected Elements team are exploring some science.First, is hair the secret to healing? We find out why trading fur for sweat may have had unexpected consequences. Then, we learn all about ball lightning – real life fireballs that, despite first being sighted over 800 years ago, remain a mystery.Next, is your garden full of rap stars? We're joined by Elizabeth MacDougall-Shackleton who tells us what we can learn from sparrows' surprisingly aggressive rap battles. We're also joined by Paulo Bittencourt who proves why we should all appreciate a nice big tree.All that, plus many more Unexpected Elements.Presenter: Marnie Chesterton Producers: Margaret Sessa-Hawkins, Lucy Davies, Alice McKee, Robbie Wojciechowski, and Nada Soufi