When newborn yukkuri says "take it easy" for the first time. Normal newborns will respond reflexively and distinctly, although usually slurred to some degree.
In the wild, parent yukkuri often use this as a "test" to see if an offspring is "easy" (a buri or premature_yukkuri will be rejected for failing to perform a greeting "properly" and killed for being an "imposter" or an "uneasy baby" or simply left to die from exposure or lack of food.
Adult yukkuri still seem to retain the "reflex" that compels them to respond to a greeting in the same way, however the extent of it varies with author or artist. In yukkuri social situations, it fulfills a similar role to accessory identification - When yukkuri individuals meet for the first time, they will exchange greetings. Individuals that do not respond correctly are either mistrusted or simply met with confusion.