Social media users believe they have cracked the meaning of the Kiwi head nod.
A Reddit post stirred discussion this week with a Kiwi user saying a Ukrainian colleague had recently asked the difference between an upward head nod and a downward nod.
"I thought about it, and it struck me that I'll nod downwards to acknowledge strangers or people I know and don't care overly much for, but I'll nod upwards for people I know and like," said the user, who then asks others for their thoughts.
The post has received more than 160 comments and been upvoted more than 700 times.
The general consensus is that nodding down is a formal acknowledgement of a person, while raising your chin is more casual and typically used when the two people are friendly.
"Nod down is a formal, 'I see you, hello' kind of nod. A nod up is a casual, 'dude! How's it going' kind of nod," one user said. "Down is acknowledge, up is 'Sup', up w/ eyebrows is 'SUP CUZ'," said another.
"Apparently the reason we do this, is because the upward nod to friends exposes our throat to them, which shows them that we feel comfortable enough around them to expose our vulnerabilities
"The opposite is true, the downward nod is an acknowledgement but it also subconsciously protects your throat."
Others debated the inclusion of eyebrows in the nod.
"The eyebrows are the most important part! You can do the eyebrows without the nod, but you can't do the nod without the eyebrows," said a poster.
One person was just surprised there was a hidden meaning.
"What the hell?! I have never thought about this for one second, no one has ever instructed me on how nods work but I do the downwards for strangers upwards for friends. How the heck does that work?"
The post also stoked discussion about other mannerisms and gestures.
"The other great one that maybe even urban Kiwis don't know about --- the rural raised-index-finger-on-the-steering-wheel acknowledgement wave when cars approach each other in the countryside," said someone on Reddit.
"It's a way of telling if you're from the city or not. If the one-finger-wave doesn't get reciprocated - you're not from 'around here'. Or at least, you don't understand rural culture."