One quirk of P.E.I.'s dialect is a sharp inhale to show agreement.

"It's not a medical condition, it's an Island non-verbal for yes," explained CBC P.E.I. weatherman Kevin "Boomer" Gallant in a video about P.E.I.-isms.

If you've ever wondered why an inhale indicates agreement, Anne Furlong, an associate professor in UPEI's English Department, has the answers.

1. It has a technical name

In linguistics, inhaling in agreement is called ingressive pulmonic speech or an ingressive particle.

"Ingressive means breathing in, pulmonic refers to the lungs and a particle is a part of speech which is not necessarily a full word like cat or dog, but which is used in conversation," said Furlong.

2. It shows more than just agreement

Inhaling in agreement is part of an informal conversation, said Furlong, so it indicates a level of intimacy. It's often used among friends, family or colleagues.

"It's a way of not just saying agreement, but also of establishing the kind of closeness and also saying, 'I don't need to do anything more than agree because we all understand the situation perfectly well,'" said Furlong.

She said it can also be used to establish an intimacy or camaraderie.

"If you're talking to an Islander and you've only met him or her for the first time, and he or she says, 'Oh yeah, yeah' [with an inhale], then you know in a sense that you've been invited inside the circle," said Furlong.

3. Its origins probably have something to do with the Vikings

The inhale probably originates with the Vikings.

It's common in Gaelic speakers, so was probably brought to the Island through Scottish and Irish immigrants that settled the Island in the 18th century.

But the origins go back further than that.

Furlong said ingressive speech has been studied for a long time in Scandinavian languages — Swedish, Norweigian, Danish and Finnish.

"We don't know whether it's … something that is native to Celtic speakers, but we do know however is that there is a long overlap — hundreds of years — between the Vikings and the northern people of the British Isles," she said.

One theory is that the Vikings brought the inhale to the Celts, who in turn brought it to Atlantic Canada.

"We do know that it is widely distributed in Scotland, Northern Ireland, parts of the north of England, which is exactly where you'd expect the people from Prince Edward Island, and parts of Nova Scotia, New Brunswick and Newfoundland, to come from."

4. It's not unique to P.E.I.

The inhale is common throughout Atlantic Canada, and Furlong said it's also used in the Ottawa Valley, where there was also heavy Scottish migration.

But the inhale is also used around the world, on more or less every continent and in many different languages. It's used in Japan, parts of Africa, and even in some indigenous Australian languages.

"We know that this could not have been done by language contact, there's just not enough possibility for this to have occurred," said Furlong.

The explanation, she said, would be that it arises spontaneously in different languages.

5. There's a reason P.E.I. claims it as its own

Islanders claim the inhale as a P.E.I.-ism, but as we now know, it's used in other parts of Atlantic Canada and other parts of the world.

Furlong said that's not surprising. Since it's used among friends, you may not hear it if you're travelling.

"If you don't hear it from somewhere else, what else would you assume? That it belongs just to you."

She said it's also something that's picked up on when people leave the Island.

"Islanders are perfectly well aware that when they move to other parts of the world — even to other parts of Atlantic Canada — they are immediately recognized as Islanders because of the way they speak," she said.

"They will assume that these words that are often picked up on by outsiders must be unique to P.E.I."