Bringing the ox bones to class surprised Koo Yung Hoi's students.
He bought the bones at a local market for 20 yuan (3 U.S. dollars), and after removing the flesh with a knife, boiled them over four days to eliminate the oil before drying them for a further five days.
More than 3,000 years ago, the Chinese used the same method to clean bones to carve inscriptions on.
Koo Yung Hoi, 55, from the Republic of Korea, teaches oracle bone studies at Henan University in central China's Henan Province.
Oracle bones are pieces of ox scapula or turtle plastron, which were used for divination during the late Shang Dynasty (1600-1046 BC). They bear the earliest significant corpus of ancient Chinese writing and contain important historical information about the Shang.
Among the 4,500 characters found on oracle bones so far, only 1,500 have been translated. Koo can read and write 1,000 of them.
"The students always see rubbings, so I brought a real one. It's easy for them to understand their ancestors' marvelous achievement in creating the earliest form of Chinese characters," said Koo, who has been teaching oracle bone studies since 2009.
Before moving to Henan University in November 2015, Koo taught oracle bone studies in Anyang Normal University. Anyang was the ancient capital of the late Shang Dynasty, and Xiaotun Village in Anyang is the place where oracle bones were first discovered.
In Anyang, Koo had the chance to touch and examine 200 oracle bones with the help of friends from the Chinese Academy of Social Sciences (CASS) archeological team. Before that he read more than 70,000 rubbings to finish his doctoral thesis on the relation between oracle bones and god worshipping in the Shang.
The appearance of Koo, wearing a leisure shirt, jeans and sports shoes, causes a stir in the traditionally conservative archeology class, with his Mandarin that has a strange Korean accent.
"I doubted he had something to offer," said Zhu Pengyu, 23, a postgraduate student. "He surely proved I was wrong."
For Hou Weidong, an associate professor of archeology in Henan University, Koo's unswerving pursuit of oracle bone studies has won his respect,
"Koo overcame the language barrier and made great achievements," Hou said. "There is no reason for us Chinese scholars to slack off at work."
Koo's journey to become a professor was not easy. Even in China, oracle bone studies is considered "lost knowledge," which few Chinese are willing to learn.
"As a foreigner, the most difficult part is the language," said Wang Yuxin, a renowned oracle bone scholar. Koo was the last doctoral student he tutored before his retirement.
"He needs to translate the elusive oracle bone scripts into ancient Chinese, then into modern Chinese, then into the Korean language to think it over, finally he needs to write papers in Chinese," Wang said. "With his pure love of Chinese traditional culture, he overcame unimaginable difficulties and fulfilled his dream."
In 1997, at the age of 35, Koo sold his apartment and car in Seoul and with 200,000 yuan starting capital began his China endeavor with his wife and two young daughters.
"My father opened a traditional Korean medicine clinic, and I learned from him the 'Book of Changes' and 'Inner Canon of the Yellow Emperor,' two major doctrinal sources of Chinese medicine," Koo said. "That's the root of my love for Chinese traditional culture."
Koo studied construction engineering in college and served in the army for four and a half years before he became a software engineer, developing foreign exchange systems for banks.
"Although it was decent pay, it was not what I wanted," he said.
In his first three years in China, he studied ancient and modern Chinese language and history as well as acupuncture in five universities in Tianjin and Beijing, and recieved a CASS master's degree in Chinese ancient history in 2003.
During his master program, Koo fell in love with oracle bone script. He received a CASS doctoral degree in oracle bone studies in 2007.
"Without the support of my father, I would never have finished my studies," said Koo, who needed 150,000 yuan each year to study and live in Beijing.
Koo once thought about giving up due to acedemic and economic pressure.
"I cannot fail Mr. Wang and make him ashamed. I was the last doctoral student he tutored," Koo said. "I cannot fail my father, either."
After a 10-year study in China, Koo went back to Seoul but discovered there was no proper job for him. He worked as a translator for a government agency for two years before being invited as a doctoral talent by Anyang Normal University, thanks to his tutor's introduction.
In 2013, Koo published his first book on oracle bones. Two years later, Koo was introduced to Henan University as a Yellow River Scholar, a post for leading scholars.
The Korean is now busy preparing his second book, "120 Years of Oracle Bone Studies in China," which is co-written with his tutor. To write the book, which will be published this year, he read every book related to oracle bone studies since the 1930s.
Koo believes China is the root of oracle bone studies, and it is the only country he can make full use of what he has learnt.
"As long as they employ me, I will stay in China as long as I can," he said.