If you've never heard it before, imagine the sound made when sucking up a drink quickly through a straw. A sharp intake of breath, with the lips kept close together (different from what in English sounds like a gasp of surprise, when your mouth is typically wider open).
Non-natives often have stories of thinking a northern Swede is shocked or has a breathing problem the first time they encounter the noise. Swedes joke that to clean under a bed or sofa, just ask your friend from Norrland to take a look under it and while they're looking, ask 'is it dusty?' A darker joke notes that the best way to kill someone from the region is to wait until they're eating, and ask if their food is good.
After The Local travelled to Umeå in 2015 to document the unusual sound, which you can hear in the video below, the northern Swedish 'yes' went viral, with media across Sweden and from the UK to Australia covering the linguistic quirk.
So we know what it sounds like, but what's the story behind the strange 'yes' noise?
First, let's look at what actually happens when you make this sound. The reason it sounds so bizarre is that most words and sounds in human speech are made by breathing out, but this is what's called an ingressive sound, meaning the speaker is drawing air in. The northern Swedish 'yes' is usually unvoiced, which means that the vocal chords don't vibrate at all when you say it.
As for what it means, as the video shows, it's a way of showing agreement or saying yes. We can narrow it down even further: a 2003 study found Swedes used the ingressive 'yes' with people, but not when they thought they were speaking to an automated machine. This suggests that it's a part of informal speech, closer to 'yep' than 'yes', but could also show that it's a way to signal acknowledgement of the speaker.
The sound isn't included in official Swedish grammar manuals, so it's hard to outline any strict rules for its usage. Linguists can't even agree on one way of documenting it: some use '.jo' with the full stop signalling inhalation, but others write the sound 'jʉ', 'schvuu', or 'schwup'.
You probably wouldn't hear the inhaled 'yes' in every situation. It tends to show agreement with what the speaker is saying, but is weaker than a spoken 'ja' or 'jo' (the two words for 'yes' in Swedish, the first generally used affirmatively and the second more often used to respond to a negated statement).
This is called backchanneling: when you respond in order to give feedback and show that you're listening and understanding without the 'turn' of the conversation being passed to you. If you've read Lord of the Flies, just think of it as the sort of response you'd give without needing to take the conch, and it can also be used to end a conversation you don't want to continue. So it makes a lot of sense that ingressive sounds would be used for this kind of marker – it's clear to the other speaker that you're not trying to interject.
Many Swedes think the sound is unique to the north of their country, and it has become a symbol of the stereotypical strong, silent Northerners, often used in TV shows and notably in advertising for Norrlands Guld beer.
In fact, you'll hear an ingressive 'yes' across across almost all of Sweden, but it's more common the further north you go. The sound also becomes more distinct in the more northern regions, which is partly because of the different words for yes in the north and south. In the south, 'ja' is the main word for 'yes', with 'jo' only used to respond to negative statements, but in Norrland 'jo' is used more frequently and in a wider range of contexts.
So ingressive yeses exist in southern Sweden too, but observers tend not to notice the relationship between this sound and the northern Swedish 'yes'. When saying 'ja' rather than 'jo', the speaker's mouth is in a more relaxed position so that even when breathing in, you can hear the soft 'j' that the word begins with.
An inhaled 'jo' on the other hand is much less clear, because the position your mouth is in, with lips almost pursed, when you say the word 'jo' leads to a sharper intake of breath. It's simply easier to say 'jo' on an inhale compared to 'ja', which might be why the sound is so common in Sweden's north.
In the Umeå variant heard in The Local's video above, there's no trace of the word 'jo' at all, although we don't know if the northern Swedish yes developed from inhaled forms of 'jo' or developed independently.
However, we do know that ingressive sounds exist in dozens of languages around the world, most often in similar contexts to the northern Swedish one, as an affirmation used informally. These inhaled yeses have been around for a very long time, although not studied in much depth.
One of the few researchers to have done so, linguist Robert Eklund who tracks ingressive speech extensively on his website, describes them as a "neglected universal phenomenon" and argues that these sounds aren't uniquely Scandinavian at all, but have cropped up independently in societies across the globe. His research notes that the earliest mention of an inhaled, affirmative sound relates to an Eskimo language and dates back to the 18th century.
Hop over the Baltic Sea from Sweden to Finland and you'll notice that in Finnish, it's possible for entire sentences to be spoken while breathing in, and both words for 'yes' are regularly said while inhaling. Ingressive sounds are also very common in Atlantic Canada (residents of Prince Edward Island also claim the sound as unique to them), parts of Maine, the north of Scotland, Ireland (sometimes grouped together as Gaelic) and Scandinavia.
Because the phenomenon is so common across the northern hemisphere, theories have developed that the sound may have travelled with the Vikings as they crossed the seas for trade and battle, or that it is a way of coping with the cold, allowing people to communicate without opening their mouths too much.
But it's also used in parts of Africa, Asia, and South America; it crops up in all inhabited continents and has been observed in pockets which are too remote and have had too little language contact with Scandinavia or Northern Canada for the sounds to be related.
Speakers of French might recognize the sound from the inhaled 'ouais' (yeah), and in parts of Argentina, you'll hear whole phrases spoken with inhalation, similar to the Finnish use of ingressive speech. Fun fact: ventriloquists are also believed to have used this kind of speech as a way of making their act more convincing as far back as the 17th century.
And if it's disappointing to learn the noise isn't unique to Swedes, it gets worse. Ingressive sounds aren't even unique to humans, with the phenomenon observed among several animals, including purring felines and calls from species ranging from monkeys to frogs.
But back to Sweden. Eklund's research has found that Swedes use the sound extremely frequently, with roughly one in every ten 'ja's said using inhalation. So sorry Swedes, your northern 'yes' isn't that unique, but it is still rather special.