A series of educational books, featuring a character called Professor Poo who helps Japanese children write and memorise hundreds of kanji characters, have become best-sellers in Japan.
The Unko Kanji Doriru (poo kanji drill) books tap into children's obsession with poo and toilet humour to help them learn.
Professor Poo is a yellow emoji-like dropping with glasses and a moustache, who provides sentence examples using the word "poo" every time: "The man took poo in his hand to face his difficulties" or "A foreign news outlet came to interview me about my poo".
The publisher, Shuji Yamamoto said his aim was to make boring study more fun - and funny.
"I'm an extremely ordinary person. So I know what most ordinary people want. I know what is likely to sell," Yamamoto tells the Mainichi Shimbun newspaper.
So far the books have sold 1.83 million copies and have become very popular with the country's primary school students.
They sell for 1058 yen (A$12.86) on Amazon, where one reviewer wrote: “My child is laughing out loud. It’s great that learning can be so funny.”
There are 2,136 regular-use Chinese-based characters, or kanji, in written Japanese, along with the hiragana and katakana phonetic scripts.
Japanese children are expected to be able to read and write 1,006 kanji by the end of their primary school years.
"Adults may raise their eyebrows, but for children, the word 'poo' is magical and makes things fun," the book's author, Yusaku Furuya, told Kyodo news.