Because from the summer of 2016, the couple from Tokyo's Tama district have been making caps for cats out of it, and created an Internet sensation.
Hiromi produces caps from molt of their three felines, and Ryo takes photos of them wearing the headgear, and posts them on an Instagram account, which has now attracted more than 80,000 followers.
They have posted pictures of more than 100 hats, including one with rabbit ears and another with a wizard-like pointed top.
The method is straightforward. To make an "acorn cupule"-shaped cap similar to a beret, a ramen-bowlful of molt is required.
The "ingredients" for the hats are provided naturally by the cats, which are three different colors. One is white, another a brown tabby and the third a gray tabby.
First, a fur ball is made by adding fluffed out hair little by little. Then, make a dent to shape it into a bowl to fit the head of a cat. Lastly, pinch the top of the hat to make pointy tip. It takes about 15 minutes.
The idea of making hats for cats with their own hair was hatched in the spring of 2016 when the Yamazakis put a chunk of molt on a cat's head, as one does, and shaped it into an extravagant Trumpesque pompadour, just for fun.
"The cats did not resist, perhaps because they were made of their own hair," said Hiromi.
In June 2017, the couple published a photo book of the hat collection.
One fan of the couple's work is Mitsuyoshi Tsujita, 46, who was inspired to make a hat with his cat's molt in about half an hour.
"I used to consider molt as rubbish," said the furniture maker from Sakai, Osaka Prefecture. "Their idea is amazing."
However, the Yamazakis are not the first to come up with the idea of making a fluffy nuisance.
Kaori Tsutaya from Tokyo’s Setagaya Ward has been advocating felting using cat hair, instead of sheep wool.
She has been holding workshops and exhibitions of cat felt works in Tokyo, Osaka and Kyoto prefectures since 2009.
Cat hair is felted by applying detergent in the same way as it is done with ordinary wool. The cat molt can be used to make needle felted dolls, or used to embroider a motif on scarves.
Felters need to keep in mind that cat hair is less hard wearing than wool, and more brittle.
Some people don't like cats. No worries. Dog hats are in too, and even humans wear those.
Hideko Tsujii, from Otsu, Shiga Prefecture, is a professional hat designer who made felt with her dog’s molt.
About five years ago, Tsujii, 54, made a beret, and wore it out. A friend liked it so much she asked if Tsujii would make her one.
Like a ball of pet hair scraped off the floor of a room, things snowballed from there.
Tsujii started up an online shop, to take custom orders for making dog-hair hats.
To make a hound hair hat for humans, a 45-liter plastic bag of the molt is required. Sheep’s wool is mixed with the dog hair as length of hair varies depending on the species of dog--short hair, such as from the Japanese shiba, are difficult to felt.
"Dogs must be pleased to be able to warm their owners with their own hair," said Tsujii.
Kaori Mizuuchi, 29 and from Suita, Osaka Prefecture, lost Lucky, a shiba she had for 17 years, in 2010. She grieved for nearly six months.
But she had been collecting the molt from Lucky for five years or so.
In 2015, she asked Tsujii to make a hat from it.
"The color and texture of the hat are almost the same as Lucky's," said Mizuuchi. "When I am wearing it, it feels like Lucky is by my side."