Furious that his son had been rude to him, a 74-year-old man attacked him and his girlfriend with a chopper.
The attack left 33-year-old Mr Benson Yuan Pei Sheng, who had hurled vulgarities at his father in a phone call, with slash wounds and a broken left wrist and forearm.
Weng Kim Song, a retiree, was yesterday jailed for 31/2 years after pleading guilty to causing grievous hurt with a weapon.
A second assault charge involving Mr Yuan's girlfriend, Ms Calinda Yeo Hui Ping, 27, was considered during sentencing, although details of her injuries were not revealed in court documents.
The incident was sparked on March 25 after Weng called his wife's mobile phone and it was answered by Mr Yuan, who was rude to him. The pair argued before the father hung up.
That evening back at their Commonwealth Close flat, he spotted his son and his girlfriend asleep in a bedroom.
He decided to confront Mr Yuan about their earlier argument and grabbed a chopper - which had a 22cm blade - from the kitchen.
Deputy Public Prosecutor Houston Johannus said: "The accused's intention of arming himself with the chopper was to slash the victim with it if he did not apologise."
Mr Yuan was angry to see his father in his room when he woke up and the pair quarrelled again before Weng attacked his son.
Ms Yeo was slashed when she tried to stop the attack by throwing a bolster at Weng.
Weng's 70-year-old wife, Madam Ho Bee Choo, rushed into her son's room when she heard the commotion and took the weapon away from her husband.
She threw the chopper out of a window of the sixth-storey flat and a passer-by alerted the police after Weng was spotted retrieving it from the ground floor.
Officers arrested him in his flat later that evening and the injured couple were taken to hospital.
DPP Johannus urged District Judge Kessler Soh to jail Weng for four years as he had caused serious injuries to his son.
Weng's lawyer, Mr Christopher Sim, who was assigned to the case under the Criminal Legal Aid Scheme, pleaded for a jail term of three years or less.
He also said that Mr Yuan is now living with a cousin and has since forgiven his father.
Court papers did not state why the father and son have different surnames.