Former council worker and fruit picker Terrence David Kain "freaked out" and strangled his elderly mother, after years of arguments about whether his smoking caused his father to die from oesophageal cancer, a court has heard.

Mr Kain has pleaded not guilty to murdering his elderly mother Beverly Kain on February 27, 2011, in a house they shared in Goulburn, but guilty to manslaughter, a plea the Crown did not accept

His defence barrister, Peter Williams, said there was no issue that Mr Kain killed his mother, but he had reduced culpability because of brain damage caused by decades of heavy drinking.

Mr Kain's sister, Debra Stinson, said that evening she received a phone call from him as she was watching television in bed.

"He said 'mum's dead, I strangled her, she's dead' and then he hung up," Mrs Stinson told the Supreme Court of NSW on Tuesday.

Mrs Stinson said she called back and her brother answered.

"I said something along the lines of 'what the hell have you done?' and he just repeated the same words 'She's dead, I strangled her, she's dead.'"

Her brother didn't sound drunk on the phone but his voice wasn't normal, she said.

"Just a very flat, very monotone voice, not much emotion there at all."

Crown prosecutor Siobhan Herbert said when police asked Mr Kain why he killed his mother, he said: "Because that's what I felt like doing to her."

Ms Herbert said Mr Kain, who has a prosthetic leg after shooting himself while drunk in 1991, used to self-harm after drinking, but there was no evidence of violence towards others.

There would be evidence about verbal fights between Mr Kain and his mother, including on the day of her death, Ms Herbert said.

"He said (to police) he and his mother had argued, he lost his temper with her.

"His mother blamed him and his smoking for having killed his father who died of oesophageal cancer."

Mr Kain told police he had about 10 stubbies of beer that night, and could not remember exactly what happened.

The jury was told Mr Kain had been drinking alcohol since he was about 16 or 17, and had been hospitalised several times.

The trial is continuing before Justice Michael Adams.