Lick Lick is a bonding and grooming behavior exhibited by yukkuri. It consists of one yukkuri (often a parent) licking another yukkuri to remove dirt, soothe injury, or otherwise clean the yukkuri.
When used for the purpose of grooming/cleaning, it's generally referred to as a "Clean clean". In several stories, Yukkuri licks have been shown to be able to relieve and heal pain even in humans. However other stories make clear that the "lick lick" ritual merely applies a thin coat of sugary water (yukkuri's drool) on the affected area. Thus, while adequate from cleaning purposes or as an effective first aid for yukkuri's small injuries, is nowhere as useful for most severe yukkuri injuries that may require treatments by humans or expert yukkuris like Yukkuri Eirin and human ones.
As with some newborn mammals, some stories also hint that newborn yukkuris are unable to feel the need for poo poo on their own. Instead, the mother yukkuri has to lick their belly and anyaru region to stimulate defecation, and later to clean the "feet" area, avoiding the spreading of dangerous mold.
A koyukkuri raised in captivity thus has to be "artificially" subjected to "lick lick", by gently rubbing it with damp cloth until it relieves itself, and then cleaned up; if not, it may develop constipation.