A psychiatric patient who slit a stranger's throat in Tai Po in February was found guilty of wounding with intent.
Chung Chi-fai was unanimously convicted by a jury of attacking salesman Wu Yuen-fai, inflicting a 25cm neck wound.
Mrs Justice Judianna Barnes Wai-ling said in the Court of First Instance yesterday: "This is a really bizarre attack. I will call for two reports to see whether the defendant suffers from psychological problems."
Prosecutors said Chung, 42, received education up to Form One and started abusing cough syrup in 1988.
He underwent psychiatric treatment at Prince of Wales Hospital in Sha Tin in 2007 and had been attending follow-up consultations since then.
The judge adjourned sentencing to November 30, pending reports on Chung's mental health. Chung was remanded in custody.
The court heard earlier that Chung, wearing a "creepy smile" on his face, walked up behind Wu, 35, who was having a meal with two others at a food stall on the night of February 15.
Chung sneered at Wu's dining companions and then slit his throat and ran off.
He had been placing bets on horse races before the assault, the court heard. He was arrested nine days later and was identified by one of Wu's dining companions in an identity parade.
Wu received emergency surgery and was treated in hospital for three days, the court heard. Because of the incident, he now has a numb right shoulder and difficulty raising his arm or turning his head.
The court heard Chung was jobless and received HK$1,800 a month in welfare payments. He had nine previous criminal convictions and was last released from jail in 2010 after serving a term for wounding.