His dormitory mate chided him for wearing slippers in their room.
They had an argument, which left construction worker Yang Yuehui (above) unhappy. He bought a kitchen knife and stabbed Mr Sun Yantao three times while he was sleeping.
Yang, 39, was jailed for a year yesterday after pleading guilty to one count of voluntarily causing hurt with a weapon on March 1.
The two Chinese nationals were in their dormitory at Upper Serangoon View at about 7pm that day when Mr Sun, who was also a construction worker, noticed that Yang had his slippers on.
He told Yang not to wear them as they would dirty the room and the pair started arguing.
When it ended, Mr Sun, 46, went to bed while Yang, still furious, went to a supermarket at Hougang Avenue 10, and bought a knife.
Yang returned to the dormitory and stabbed his sleeping victim three times - once on his abdomen and twice on his left upper thigh.
He then ran out and threw the knife into a nearby canal.
Mr Sun staggered out of his room to seek help. He met another colleague and together, they went to their safety coordinator, Mr Alagesan T. Mumgan, who called the police.
Mr Sun was rushed to Changi General Hospital, where he was operated on for his abdominal wound. He was discharged three days later and was given 18 days of hospitalisation leave.
For voluntarily causing hurt with a weapon, Yang could have been jailed for up to seven years and fined or caned or given any combination of such punishments.