The bell on Kettu eggs makes them easy to find when they're missing.
Kettus live somewhat challenging lives, as their tail grows bushier and bushier with each evolution. Eventually, it becomes such a challenge that it is difficult for them to traverse the wild alone as their tail is so prone to getting stuck and tangled in things. For this reason, some Arkians employ "Kettu walkers" that are trained to help keep Kettu tails safe and free from entanglement while they're outside playing.
Kettu grooming is also a competitive sport in Ark City. Groomers will compete to design the most elaborate of shapes and real-life imagery with a Kettu's tail hair.