EXTRACTING arcane messages from artistic creations is the bread-and-butter activity of your average conspiracy theorist. But nobody has ever satisfactorily explained to me how a musician or recording engineer manages to insert a message that sounds entirely innocent when played forward, but when played in reverse is transformed into a menacing slogan.

And, more to the point, if you were to go to all the trouble, why not spend a bit more time making the message intelligible rather than an incoherent drawl?

Such was the fascination of Paul is Dead (Radio 4, Tuesday of last week) that these and many more thoughts came to mind as we heard the story of Paul McCartney's death, rumours of which spread in late 1969, just at the point when the band was showing signs of wear and tear.

The first seed was planted by a caller to a US radio phone-in, by a student claiming that Paul had been killed in a car accident in 1966, and been replaced by an orphan from Edinburgh, William Campbell. The rumour spread amongst gullible Beatles devotees who had experienced a decade or more of political and social upheaval.

And, of course, it's plain to anybody with ears to hear, that the end of "I am the Walrus" played backwards conceals the message "Ha-ha, Paul is dead."

Matt Thompon's documentary was a joy: full of bonkers theories, and plenty of archive material. And, in case you thought that this was all a bit of a laugh, there was Professor Diane Purkiss, of Oxford University, to remind us that conspiracy theories are, in fact, one of the most dangerous aspects of the modern media age. At best, they paralyse democratic engagement with real political issues; at worst, they lead to violence and persecution.

As Roland Barthes would have it, myth empties reality and impoverishes history. Or, in laymen's terms, real life is both more surprising and more banal than anything one could invent. With this perspective, Peter Conrad has been exploring 21st-century mythologies in a series of weekday essays on Radio 4.

The disappearance of Flight MH370 in March makes for an obvious subject in this respect. The lack of any answer to the mystery allows in any number of mythologies, most of them subsequently discredited: Iranian passengers travelling on false passports, a disgruntled pilot, overheated Lithium batteries in the hold. The fact that an aeroplane can still disappear, despite all our satellite technology, serves, in Conrad's words, to "re-medievalise" the world.

Not all of Conrad's subjects have been as intriguing as this. On Thursday, he turned the same weighty analytical gaze on the "selfie"; a phenomenon so ubiquitous that even heads of state are taking them, and a term so popular that The Oxford English Dictionary named "selfie" as its word of the year in 2013.

Conrad's discussion ranged from the self-obsession of Narcissus to the parenting skills of Kim Kardashian. But, in reality, is a selfie not much more than a convenient way of having your picture taken without having to get somebody else to do it for you?