A yukkuri says the trademark phrase "Munch-Munch, Happiness!" when they eat something delicious. Often shown as a reflex and a yukkuri can't hold back on saying it when they eat something good. If they're eating a sweet sweet then they might say "Sweet-Sweet, Happiness" instead.
There have been known attempts at disciplining a yukkuri to not say "munch munch, happiness!" when eating but it's shown that not being able to say those words can cause stress to a yukkuri.
This tag implicates eating and happy (learn more).