There's a good chance you've probably seen the TikTok video of an American student trying to make sense of Irish people's weird way of saying "yeah" with an inward breath.
Failing that, odds are you've either done it yourself, you've heard someone else do it, or someone you know (probably not from Ireland) has heard it and didn't exactly know what it was. For the sake of clarity, here's the TikTok video explaining the whole phenomenon.
So, what is it? Well, there's actually a word for it - ingressive sound. Essentially, it's when you breathe in as you pronounce a word. Ingressive sounds are actually very common - they're just not common in the English language. However, there's one place where they're extremely common - in Scandinavian languages. In fact, if you check out the Wikipedia article for ingressive sounds, you'll hear a recording of a Norwegian person saying "Yeah" and it sounds basically like your mother saying "Yeah".
As you probably know, Ireland was regularly raided by the vikings and they established settlements in Dublin and along the coasts of Ireland, as well as intermarrying with local warlords and chieftains to forge alliances. In Dublin alone, there's a number of streets and lanes that carry Nordic names.
Not only is it common in Scandinavian languages, the ingressive affirmative - to give it the full technical term - is also very common with Newfoundlanders and the Maritimes of Canada. Why there, you ask? Well, Newfoundland has many connections with Ireland. In fact, one of the earliest accounts of Newfoundland's discovery comes from the Voyage of St. Brendan, who sailed to Newfoundland from Kerry in the sixth century.
The ingressive affirmative - yes, we're going to call it that instead of "yeah" - is an example of a pulmonic ingressive, which means that the sound comes from the lungs, not the lingual ingressive, which comes from the restriction of the vocal tract.
Every day's a school day, folks.