grass dango
A wild/stray parent yukkuri will sometimes chew a bunch of grass and leaves into a ball-like lump, which they call "grass dango" (dango being a ball-shaped japanese snack). The purpose is to soften them up and use the parent's saliva to give them a slightly sweet taste, making a healthy and delicious meal for their koyukkuri children.
If you see wild/stray yukkuris (especially koyukkuris) eating green ball-like lumps then it's probably grass dango.