Sneezes, wheezes, runny noses and red eyes - this episode is all about allergies.

An allergic reaction is when your immune system reacts to something harmless – like peanuts or pollen – as if it was a parasitic invader. It’s a case of biological mistaken identity.

Professor Judith Holloway from the University of Southampton guides our sleuths through the complex immune pathways that make allergies happen and tells the scary story of when she went into anaphylactic shock from a rogue chocolate bar.

Professor Adam Fox, a paediatric allergist at Evelina Children’s Hospital, helps the Drs distinguish intolerances or sensitivities – substantial swelling from a bee sting, for example - from genuine allergies. Hannah’s orange juice ‘allergy’ is exposed as a probable fraud!

Hannah and Adam explore why allergies are on the increase, and Professor Rick Maizels from the University of Glasgow shares his surprising research using parasitic worms to develop anti-allergy drugs!

Contributors: Professor Judith Holloway, Professor Adam Fox, Professor Rick Maizels

Pi is the ratio between a circle’s diameter and its circumference. Sounds dull – but pi turns out to have astonishing properties and crop up in places you would never expect. For a start, it goes on forever and never repeats, meaning it probably contains your name, date of birth, and the complete works of Shakespeare written in its digits.

Maths comedian Matt Parker stuns Adam with his ‘pie-endulum’ experiment, in which a chicken and mushroom pie is dangled 2.45m to form a pendulum which takes *exactly* 3.14 seconds per swing.

Mathematician Dr Vicky Neale explains how we can be sure that the number pi continues forever and never repeats - despite the fact we can never write down all its digits to check! She also makes the case that aliens would probably measure angles using pi because it’s a fundamental constant of the universe.

Nasa mission director Dr Marc Rayman drops in to explain how pi is used to navigate spacecraft around the solar system. And philosopher of physics Dr Eleanor Knox serves up some philoso-pi, revealing why some thinkers have found pi’s ubiquity so deeply mysterious.

Why are some smells so nasty and others so pleasant? Rutherford and Fry inhale the science of scent in this stinker of an episode.

Our sleuths kick off with a guided tour of the airborne molecules and chemical receptors that power the sense of smell. Armed with a stack of pungent mini-flasks, professor Matthew Cobb from the University of Manchester shows Hannah and Adam just how sensitive olfaction can be, and how our experience of some odours depends on our individual genetic make-up.

Dr Ann-Sophie Barwich from Indiana University reveals how most everyday smells are complex combinations of hundreds of odorants, and how the poo-scented molecule of indole turns up in some extremely surprising places.

With the help of a flavoured jellybean and some nose clips, Hannah experiences how smell is crucial to flavour, adding complexity and detail to the crude dimensions of taste.

Speaking of food, listener Brychan Davies is curious about garlic and asparagus: why do they make us whiff? Professor Barry Smith from the Centre for the Study of the Senses reveals it's down to sulphur-containing compounds, and tells the story of how a cunning scientist managed to figure out the puzzle of asparagus-scented urine.

Finally, another listener Lorena Busto Hurtado wants to know whether a person’s natural odour influences how much we like them. Barry Smith says yes - we may sniff each other out a bit like dogs - and cognitive neuroscientist Dr Rachel Herz points to evidence that bodily bouquet can even influence sexual attraction!

How do winds start and why do they stop? asks Georgina from the Isle of Wight. What's more, listener Chris Elshaw is suprised we get strong winds at all: why doesn't air just move smoothly between areas of high and low pressure? Why do we get sudden gusts and violent storms?

To tackle this breezy mystery, our curious duo don their anoraks and get windy with some weather experts.

Dr Simon Clark, a science Youtuber and author of Firmament, convinces Adam that air flow is really about the physics of fluids, which can all be captured by some nifty maths. The idea of pressure turns out to be key, so Hannah makes her own barometer out of a jar, a balloon and some chopsticks, and explains why a bag of crisps will expand as you walk up a mountain.

Professor Liz Bentley, Chief Executive of the Royal Meteorological Scoiety, reveals how the dynamics of a simple sea breeze – where air over land is heated more than air over water – illustrates the basic forces driving wind of all kinds.

Then everyone gets involved to help Adam understand the tricky Coriolis effect and why the rotation of the Earth makes winds bend and storms spin. And Professor John Turner from the British Antarctic Survey explains why the distinctive features of the coldest continent make its coastline the windiest place on earth.

DO WE HAVE YOUR ATTENTION?

Good! But how does that work!?

Our intrepid science sleuths explore why some things immediately catch your eye - or ear - while others slip by totally unnoticed. Even, on occasion, basketball bouncing gorillas.

Professor Polly Dalton, a psychologist who leads The Attention Lab at Royal Holloway University, shares her surprising research into ‘inattentional blindness’ - when you get so absorbed in a task you can miss striking and unusual things going on right in front of you.

Dr Gemma Briggs from the Open University reveals how this can have dangerous everyday consequences: you are four times more likely to have a crash if you talk on the phone while driving -even handsfree.

Drs Rutherford and Fry also hear from stroke survivor Thomas Canning, who developed the tendency to ignore everything on the left side of space, despite his vision being totally intact.

And Dr Tom Manly, from the University of Cambridge’s Cognition and Brain Sciences Unit, helps our sleuths unpack the neuroscience of this fascinating condition.

Chi Onwurah tells Jim Al-Khalili why she wanted to become a telecoms engineer and why engineering is a caring profession.

As a black, working class woman from a council estate in Newcastle, she was in a minority of one studying engineering at university in London and encountered terrible racism and sexism. She went on to build digital networks all over the world, the networks that make today's instant muli-media communications possible. And Chi built the first mobile phone network in Nigeria, when the country was without a reliable electricity supply. Today she is Shadow Minister for Science, Research and Innovation.

When Chi decided to go into politics, her engineering colleagues were not impressed. Why would anyone leave their noble profession to enter a chaotic, disreputable and dubiously useful non-profession, they asked. But, Chi believes, parliament desperately needs more scientists and engineers, not only to help us solve science-based problems but also to create technical jobs and build a strong economy.

Six and a half million dead. More than a hundred times that infected. The Covid-19 pandemic has wreaked havoc across the globe. But in the final months of the third year of this health crisis, some now claim it’s all over.

Scientists with key roles in the global response join Claudia Hammond to consider the evidence behind the declarations that the pandemic has finished and they set out how, officially, this global health crisis will be brought to an end.

They reject claims that the pandemic is over, but say the emergency phase of this global health crisis is coming to a close.

But only if countries remain vigilant and maintain pandemic preparedness.

If vaccines reach arms, if treatments are shared equally and if nations re-introduce public health measures like mask wearing and social distancing when the inevitable new waves (and potential new variants) emerge, the appalling loss of life we saw at the beginning of the pandemic, they tell Claudia, won’t be repeated.

There are stark warnings too that the dramatic global drop in the sequencing of virus samples (which enables us to see how the virus is evolving) is posing a serious risk.

We can’t react to a new threat, Claudia’s panel say, if you can’t see it. Sequencing, as well as testing, has fallen by 90% since January this year, from 100,000 weekly sequences ten months ago to less than 10,000 now. This severely limits the ability to track the known variants (currently 200 sub-lineages of the Omicron variant).

Produced in collaboration with Wellcome and recorded in front of a live audience in Wellcome’s Reading Room in London, Claudia’s expert panel includes Dr Maria Van Kerkhove, the World Health Organisation’s Technical Lead for Covid-19, Professor Salim Abdool Karim, co-chair of the south African Ministerial Advisory Committee on Covid-19 and a member of the Africa Task Force which oversees the African continent’s response to the virus and Professor Sir Jeremy Farrar, the Director of Wellcome and a former adviser to the UK government on its Covid response.

Presenter: Claudia Hammond

Literature student turned neuroscientist, Prof David Eagleman, tells Jim Al-Khalili about his research on human perception and the wristband he created that enables deaf people to hear through their skin. Everything we see, taste, smell, touch and hear is created by a set of electro-chemical impulses in the dark recesses of our brain. Our brains look for patterns in these signals and attach meaning to them. So in future perhaps we could learn to ‘feel’ fluctuations in the stock market, see in infra-red or echo-locate like bats? Each brain creates its own unique truth and David believes, there are no real limits to what we humans can perceive.

Nobel Prize winning chemist Frances Arnold left home at 15 and went to school ‘only when she felt like it’. She disagreed with her parents about the Vietnam war and drove big yellow taxis in Pittsburgh to pay the rent.

While some colleagues accused her of intellectual laziness, industry jumped on her ideas and used them in the manufacture of everything from laundry detergents to pharmaceuticals.

Who could forget the beginning of 2020, when a ‘mysterious viral pneumonia’ emerged in the Chinese city of Wuhan. Soon, other countries were affected and deaths around the world began to climb. Perhaps most alarmingly of all, there were no proven treatments to help prevent those deaths.

As the World Health Organisation declared the Covid-19 outbreak a pandemic, and the UK and the rest of the world braced itself for what was to come, doctor and drug-trial designer Martin Landray had his mind on a solution, devising the protocol, or blueprint, for the world’s largest drug trial for Covid-19.

As Professor of Medicine and Epidemiology at Oxford University, Martin was perfectly positioned to jump, delivering what became known as the RECOVERY Trial. The trial was tasked to deliver clarity amid the predicted chaos of the pandemic and galvanised every acute NHS hospital in the UK. Within its first one hundred days, it had yielded three major discoveries and it has transformed Covid-19 treatment worldwide, already saving over a million lives. Sir Martin Landray was recently knighted for this work and RECOVERY’s legacy lives on, not just for Covid. Martin plans to revolutionise drug trials for other diseases too.