There is a Japanese nursery rhyme called:
“Donguri Korokoro” (The Falling Acorn)
In this song, an acorn falls off the tree and rolls into a pond. In the world of onomatopoeia, the continuous rolling movement of something small and round is referred to as “koro koro”.
For instance, when a worn-out eraser with rounded edges rolls off a desk in the middle of an exam, “koro koro” is the first sound that comes to mind. You might also want to indulge in an extra bit of imagination here – “koro koro” is the sound of tiny kitten fluffballs play-wrestling, or even golf balls bumping and rolling across the green. It’s cute, but at the same time, a little clumsy.
But when the rolling object becomes bigger and heavier, we tend to say it moves in a “goro goro” manner instead. Like big rocks falling from the top of a mountain, logs rolling off truck beds, or a heavy watermelon or pumpkin tumbling off an overstocked supermarket shelf in the fresh produce department.
That’s not all. We also use “goro goro” to talk about the movement of people or animals when they’re lying down, tossing and turning from left to right in a completely relaxed state of “I-don’t-care”.
During the weekend, if you tell your friends you’re just planning to “goro goro”, they’ll know not to impose on your me-time, where you’ll be lazing around at home, spending the entire day doing absolutely nothing but rolling around in your pajamas.