The two human characters who were part of this Odemon examined audio recordings. They were audio scientists, which I assume is a thing.
“We’re finally close to cracking the Jynx language, I can feel it,” human one said.
Human two looked at the Jynx in the lab. “We’ll finally learn what secrets these weird Pokemon are saying.”
Every time either of them said something a Jynx spoke up with, “Jynx.”
Which was annoying when they were listening to recordings of Jynx so they stopped talking as they pieced together the last bit of the Jynx’s incomprehensible language. But incomprehensible no more, for by reordering the sound they determined what the Jynx were really saying! It was a historic moment as they played the new recording back, and understood the Jynx for the first time as it played:
“Jinx, you owe me a soda.”
The two humans looked at the Jynx in the lab.
“What?” asked one, while at the same time a Jynx said, “Jynx.”
The two humans looked at each other.
“You know what, I think Jynx actually communicate through dancing.”
“Yes, that makes more sense, it’s the universal language probably maybe.”
And they destroyed all record of the work they’d done there. For if every time Jynx spoke someone owed them a soda… No. The human race’s soda reserves were too valuable to risk it.

-Odemon #124 Jynx