Wake up! It’s time for a dreamy new episode of Curious Cases all about the science of sleepwalking.

Listener Abigail has done some strange things in her sleep, from taking all the pictures off the wall, to searching for Turkish language courses. And she wants to know: WHY IS THIS HAPPENING?

It turns out Abigail is not alone. Hannah and Dara hear weird and wonderful stories of extreme sleepwalkers - from the lady who went on midnight motorbike excursions, to the artist who does all his best work while asleep. They delve into the neuroscience to find out how you can remain in deep sleep while walking, talking or even peeing in your mum's shopping basket. They learn about some cutting edge research where the participants were sleep deprived and then half-woken with scary sounds, and they zero in on the key triggers, from a boozy night out to a squeaky bed.

Contributors

Producer: Ilan Goodman

Fruit-powered batteries are the ultimate school science experiment, but they’re normally used to power a pocket calculator. This week’s listener wants to know if they could do more, and sends the team on a quest to discover whether they could used to send a rocket into space?

Professor Saiful Islam is the Guinness World Record holder for the highest voltage from a fruit-based battery, but disappoints the team when he reveals they produce very little power. He used 3,000 of them and only managed a measly 2 Watts. Given that spaceships are famously difficult to get off the ground, it seems a lemon battery might just fail the acid test.

Author Randall Munroe is undeterred and suggests alternative ways to get energy from citrus, including burying them to make oil. Then the team discuss the pros and cons of switching to a lemon-based diet.

For battery expert Paul Shearing, all this raises a serious question, about how we will power the planes of the future. He suggests solar power could play a part in short-haul flights and discusses some of the exciting battery materials being tested today.

Contributors:

Randall Munroe, author

Producer: Marijke Peters

Are you more of a rhino or a kitten? More like a tortoise or a hare? Listener Ivy wants to know what makes a good athlete and so Hannah and Dara tackle the science of sport.

Our curious duo get to grips with the rigours of training tailored for endurance events vs those based on more explosive bursts of activity. They consider the contribution of genetics, fast vs slow twitch muscle fibres, the unique advantage of Michael Phelps's body proportions and whether butterfly really is the most ridiculous stroke in swimming.

And after a rigorous scientific analysis, Dara turns out to be ideally suited for…netball. Much to his surprise.

Contributors

Producer: Ilan Goodman

Listener Vivienne has heard that tardigrades - aka moss piglets - have special powers of survival. Radiation? Drought? Extreme cold? NO PROBLEM. Does that mean they could survive an apocalypse? And could they even help us master space travel!?

Hannah and Dara learn how to find these little moss piggies in roof gutters and garden corners. And they're amazed by their capacity to dry out and hunker down for decades before springing back to life. But calamity strikes when it turns out that fine glass tubing - in the form of pipettes - is their natural predator. And worse is to come: our curious duo learn that there may be some tardigrades stuck on the moon, and one researcher has even fired them out of a gun. All in the name of science.

But they have survived at least 5 mass extinctions so far. So their chances of surviving the next one are pretty good. As long as pipettes aren't involved.

Producer: Ilan Goodman

If there’s one type of discharge you really want to avoid, it’s lightning, but what happens when it hits you?

We hear from lightning survivor Kerry Evans, and discover that the best place to shelter – if you ever find yourself in a similarly charged storm – is in a car, or low to the ground. And why this is never a good time to take a selfie.

Dr Dan Mitchard from Cardiff University’s excitingly-named Lightning Lab explains why there's no lightning at the poles, and the presenters lament that polar bears and penguins are missing out.

We all know about the gods of lightning, but the mysticism doesn't stop there. Above cloud level there are many other types of unusually-named phenomena, reaching to the edge of space, including sprites, trolls and even pixies.

And Professor Karen Aplin reveals that lightning has even been discovered on other planets, in a science story that could affect our plans to colonise Mars.

Contributors:

Dr Daniel Mitchard, Lightning Laboratory, Cardiff University

Producer: Marijke Peters

11 year old Esther visualises days of the week in a kind of 3D structure. It’s something called ‘synaesthesia’ and she wants to know why it happens - and why other people don’t experience things the way she does.

Hannah Fry and Dara Ó Briain explore the vibrant and varied ways different people experience the world, from the man who tastes individual words - including all the stops of the tube - to the composer who sees music in shapes and colours.

And along the way, they figure out why Mozart is white wine while Beethoven is red.

Contributors:

Professor Julia Simner: Professor of Psychology,University of Sussex

Producer: Ilan Goodman

It’s sometimes said that timing is everything and this week the pair investigate the mystery of rhythm, discovering why some of us might be better at staying in tempo.

From the daily cycle of dawn and dusk to sea tides and circadian clocks, rhythm governs many aspects of our lives, and cognitive psychologist Dr Maria Witek says it makes sense we also place great importance on its presence in music. She specialises in ‘groove’, or the feeling of pleasure associated with moving to a beat – and it’s not just something the dancers among us enjoy; groove has even been used to treat patients with Parkinson’s Disease.

Neuroscientist Professor Nina Kraus has studied drummers’ brains and found their neurons fire with more precision. She explains that teaching kids rhythm can improve their language and social skills. But no need to take her word for it, because Skunk Anansie’s drummer Mark Richardson is in the studio to put Hannah to the test. Can she handle a high hat at the same time as a snare?

Contributors:

Producer: Marijke Peters

9 year old listener Koby sends Hannah and Dara on a mission to find the shiniest thing in the world. And so they enter a world of mirrors…

The journey takes them into the subatomic goings on of shiny metal surfaces, where electrons waggle and dance and send light waves back at *just* the right angle. Our curious duo play with an astonishingly reflective plastic film that can be found hidden in devices we all use. And they probe the mysterious power of refraction, harnessed to make the $2 million mirrors which reflect the lasers at the huge LIGO experiment.

And everyone ponders the surprisingly reflective properties of a pint in space.

Contributors:

Dr Felix Flicker: University of Bristol, author of The Magick of Matter

Producer: Ilan Goodman

Would you eat food that fell on the floor? That’s the question Hannah and Dara are getting their teeth into this week as they put the so-called ‘5 second rule’ through its paces.

For some people it’s 3 seconds, and for others its 10 – especially if it involves a dropped ice cream and a screaming child. But microbiologist Don Schaffner says there’s no safe amount of time to leave food on the floor if you’re planning to eat it. And while you might think buttered toast would pick up the biggest number of bugs, it may surprise you to hear that wet foods like watermelon are actually the worst when it comes to attracting harmful bacteria.

For home hygiene guru Sally Bloomfield it’s all a question of being a bit more clever about the kind of germs we expose ourselves to and weighing up risks.

Contributors:

Dr Don Schaffner: Rutgers University

Producer: Marijke Peters

While chatting at the back of class, best mates Abi and Sofia got curious about bubbles. How do you make really giant ones? Could you even get one around the entire planet?

Hannah and Dara set out to investigate. They hear from a renowned 'bubbleologist', and learn how NASA helped him blow his way to a world record. They coax a physicist to reveal the secrets of his peer-reviewed bubble-juice formula, and investigate how bubbles work in space and in the ocean.

Our curious duo also discover an audacious project aiming to build a Brazil-sized raft of bubbles... in space!

Contributors:

Dr Helen Czerski, UCL

Producer: Ilan Goodman