What unusual activity does the Chinese soft-shell turtle perform with its mouth?

They excrete most of their body's urea through their mouth. As yucky as this sounds, it seems better than how my cat cleans her bum or things my dog eats... A research team in Singapore did an experiment to see what was happening when the turtles had their head in a puddle for over an hour. They set up an experiment with the following results:

To find out what was being excreted from the mouth, the team perched the turtles beside a tank of water which acted as the "puddle" for them to dunk their heads in. They would spend between 20 and 100 minutes with their heads submerged and, while this was occurring, the team witnessed the turtles engaging in a "rhythmic throat movement characteristic of buccopharyngeal respiration"; the turtles were breathing, as well as swirling the water around their mouths. After submersion, the team measured the urea present in the tank and found that it was up to 50 percent higher than the rate of excretion via the cloaca. The turtles were simultaneously breathing, and contracting their throats to excrete urea from their mouths.

https://www.wired.com/story/chinese-turtles-urinate-from-mouths/