Narwhal mouths are on the right side of their head. In fact, some people didn't think they had mouths at all because they weren't looking from the right. Rookie mistake.
How did we know to look from the right, though? Because of the youths (ゆう). Youths think in ways that older people usually don't. That's why they can see the swirls on cereal, hear the music behind noise, and of course, look at things from the right side.