A man has been described as looking "demented" by his dad, after being accused of decapitating his elderly mum.
Philip Tarver, 47, allegedly stabbed the pensioner with an ornamental sword before threatening to kill his dad.
Tarver has been accused of attacking Angela Tarver, 86, at the family home in Woking, Surrey, on December 19 last year.
His 84-year-old father Colin gave evidence and described his son's alleged strange behaviour.
He said his son had drank a carton of beer and a bottle of vodka the night before, reports Mirror Online.
In the morning, the defendant emerged wearing "female attire", jurors heard.
Mr Tarver said: "He was wearing a short transparent petticoat type of thing. He would occasionally wear female clothing.
"He started speaking in a whisper. He was whispering about the beer. He pointed to the carton, asked me to take it back to the shop.
"He whispered 'it's poisoned'."
Mr Tarver told jurors his behaviour was "entirely unusual" as he had never said anything like it before.
His son went on to unplug household devices saying he was "spring cleaning" before going upstairs with a headache, jurors heard.
The witness said: "Later I went into the lounge and discovered the television and the recorders were disconnected as well.
"I went upstairs to find Philip and he had gone into the spare bedroom and was lying on the bed.
"I asked him what on earth was he doing, why was he pulling all these cables out.
"He jumped off the bed and angrily shouted at me and pushed me out of the room and slammed the door."
At noon, Mrs Tarver was sitting in the kitchen drinking a mug of tea and Mr Tarver was in the lounge reconnecting the television so they could watch Bargain Hunt.
This was when he heard a scream, Mr Tarver said.
"I stopped what I was doing, crossed the lounge to the dining room, could see the kitchen, see the chair Angela was sitting on was gone and all I could see was her legs resting on the chair," he told the court.
"The chair had gone backwards. She was on her back."
When he got to the kitchen door, he noticed the defendant holding a sword.
He said: "He looked strange, demented. His eyes were a yellow colour. He said 'I've got to kill you.'
"He did not look normal. I thought he was going to kill me."
When he asked him why, Tarver allegedly said he had been "commanded" to.
The witness went on: "It just didn't make any sense.
"I grabbed hold of the blade. It was only a replica sword, it was not sharp, so I grabbed hold of it with both hands, wrestled with him for several minutes until I got hold of the sword."
Mr Tarver then ran down to the end of his driveway and dialled 999.
Before police arrived, the defendant allegedly decapitated Mrs Tarver and put her head in the kitchen freezer.
He also cut off her left ring finger and put it into a kettle, the Old Bailey has heard.
When armed police arrived, Tarver came to the front door waving a Union flag and holding a knife, saying: "I surrender, I surrender", jurors have heard.
Mr Tarver said he married Angela in 1960 and Philip was the youngest of their three children.
In 1991, Mrs Tarver suffered a severe stroke which affected her mobility and speech, he said.
Unemployed Tarver denies murder and making a threat to kill his father.