The whistle

Raising her hands to her face, she stuck both forefingers into her mouth like Dracula fangs. Breathed in, blew out and emitted a shriek that could shatter a kidney stone.

'That's the whistle,' our host Eusebio explained superfluously. 'That's how you make the noise. First you learn how to do that, then you learn how to say things.'

He was talking about the famous whistling language, of course, the silbo gomero, that used to ring across the deep, wrinkled valleys of La Gomera. No wonder the Spanish conquistadors had such a bad time trying to crush these people, the whistle alone would be enough to send any sane soldier scuttling back to his troopship, chainmail ringing.

We were gathered in our neighbour's house in the village to celebrate the arrival of the new year, many years ago, when conversation turned to the silbo. It took a few glasses of wine to get Luzma loosened up enough to perform, being a little shy in front of these two foreigners, although she knew us well enough by then.

'Say something, Luzma,' Eusebio commanded. Luzma was okay now, the first whistle had relaxed her like a steam engine shedding pressure. She poked her fingers into her mouth again. This time her whistling was modulated, a tuneful warble like a blackbird singing into a Rolling Stones amplifier. When it finished our host Eusebio got to his feet, took the wine bottle from the table and topped up her glass. She warbled again, briefly.

'She was asking you to...'

'Refill her glass. Then she said, thank you Eusebio.'

Luzma was whistling again with an oddly mischievous expression. Eusebio listened, said 'Uff!' then sat down, shaking his head and pretending to be shocked. His wife Carmela explained, chuckling: 'She told him to drop his trousers to see what's inside.' Luzma cracked up with laughter. Country humour soon turns earthy.

Many of the earlier-generation Gomerans such as Luzma can still do the silbo and most can understand it. Sadly, you rarely hear it in the streets these days, although sometimes a guy will hail a friend across the town square: 'Juanito! Come and have a beer.'

As a tourist you're most likely to hear the whistle as a demonstration in a restaurant. That's fine, it's genuine enough, no play-acting or deceit, but there's an obvious risk that the silbo could turn into a cabaret act. It could forget its roots and become as false as the Disneyland flamenco dancing you can suffer in any Spanish tourist hotel.

I suppose even that would be better than the alternative, that it should fade and die, supplanted by the mobile phone. But the good news, the really good news, is that the Gomerans and the world in general realised in the nick of time what they'd got here and set about saving it. Schoolchildren now learn the silbo as part of their weekly curriculum. Even better, it has gained global recognition as a UNESCO Intangible Cultural Heritage of Humanity, which will ensure funding and support although it sounds a bit posh for what Luzma does.

Now and again the council runs a competition for young whistlers from the local schools and colleges. And they are very, very impressive. If you don't believe the silbo is really a language, watching one of these competitions will convince you. The participants compete as teams of two, a whistler and a listener. The whistler is handed a slip of paper with a message typed on it. The messages are pulled at random from a box and the competitors have no idea what they are until they're handed the paper slip. And the messages are not about galleons on the horizon or goats falling into crevices, they're things like:

Romina, we're going to the beach this afternoon, come with us and bring your radio.
Rafael, tell Rubén I met his brother and he wants to borrow his bicycle tomorrow.

The listener can request – by whistling, of course – a repeat of anything they haven't understood, then they have to say aloud what the message was. Mostly they get it right, either completely or nearly. It's astonishing.

How does it work? There are learned books and research papers about this, but basically the silbo is a phonetic representation of the Spanish language. You can hear that in the sound of it, a warble that mimics the words and intonation of the spoken language. A skilled silbador, a whistler, can represent at least four of the spoken vowels individually and perhaps all five. The consonants are mostly doubled up, one sound for two or more consonants, but that's good enough to be perfectly intelligible.

And no, I can't do it. I would love to be able to whistle across the square 'Hey, Antonio, fancy a beer?' but so far I haven't even managed the carrier signal, the raw noise. A local expert who knows everything about Gomeran culture showed me how to whistle by mouth alone, no fingers: 'Roll your tongue into a tube – like this – then put it behind your teeth and...' There it was, the piercing blast.

If you really want an ear-splitter though, to reach across a ravine, you poke one knuckle into your mouth while the other hand cups around it to focus the sound. I've tried everything, one knuckle, two fingers, tongue rolled like a cigar, but all I produce is a damp hiss or a bat squeak. Maybe Gomerans are born with some special gadget behind their teeth.