The frog had a projecting eye and hind leg. These features were lined up with the fracturesForensic pathologist Dr Richard Jones
His body, which was still wearing his Marks and Spencer pyjamas, was only discovered 18 years later - three weeks after 74-year-old Mrs Sabine died from cancer and her home was being cleared out last November.
Mr Sabine was 67 when he was last seen alive at the couple's home in the village of Beddau, near Pontypridd, South Wales.
A post-mortem examination carried out by forensic pathologist Dr Richard Jones found the cause of death was blunt force trauma to the head, although the date of Mr Sabine's death was unknown.
Dr Jones said: "The frog had a projecting eye and hind leg. These features were lined up with the fractures.
"A single blow from this item could have accounted for all the skull fractures. They are severe injuries and can easily account for death.
"The frog weighed 1.1kilo and was 14 centimeters long. The shape of the frog matched the fractures."
Dr Jones said the body was wrapped in "many layers of heavy-duty material" such as roofing felt, as well as shopping bags and bin bags tied with green string.
He said: "The decomposed body was clad in Marks & Spencer pyjamas.
"It was relatively well-preserved because of a process known as 'chemical mummification', which occurs in certain circumstances. It can persist for years or even centuries."
Mr Sabine was identified by a hip replacement he had in the 1990s, which was preserved in his skeleton. The skull had several fractures, but there were no other injuries.
Tests on his body showed he had drunk alcohol before his death, but would have been below the drink-drive limit.
The inquest heard Mrs Sabine told a neighbour she had bought a "medical skeleton" while she was training to be a nurse.
But, shortly before Mr Sabine's death from cancer in October last year, she asked the neighbour to help move it from the garden shed to the attic.
Mrs Sabine looked after the communal garden at the apartment block and the body was in her shed.
The inquest heard she shared jokes "for years" with neighbour Michelle James about it and, when it was suggested it was real, she laughed: "You never know."
After Mrs Sabine's death, neighbours began moving her belongings. They cut the packaging around the skeleton before they realised it could be human.
The inquest heard that a few months before she died, Mrs Sabine was having her hair done by hairdresser Bernadette Adamiec when she told her: "People are going to talk about me after I have gone. I could be famous."
When Ms Adamiec asked why, she replied: "Because of the body in the bag."
She said her husband was abusive and a womaniserFriend Lynne Williams
Police Community Support Officer Gareth Bishop said he was called to the house after the discovery of the skeleton and described "a strong rotting smell, like from a compost bin".
The discovery was made 25 days after Mrs Sabine died of brain cancer in October 2015.
The couple emigrated to New Zealand in the sixties, but returned to Britain in the 1980s, leaving their five children behind.
South Wales Police said Mrs Sabine was the main suspect in the death of her husband.
The inquest was told by a South Wales police officer that Mrs Sabine was "likeable, but not someone I'd trust".
Pc Joy Nicholls described her as "clearly a very strong character" in several conversations over the years.
She added: "She had referred to her husband as a b*****d. She said she was estranged from her family, but didn't want to talk about."
Her friend Lynne Williams said in written evidence that she "felt fooled" by lies Mrs Sabine had told about her background.
Mrs Williams said: "She said her husband was abusive and a womaniser."
John Sabine was last seen alive at the couple's home in the village of Beddau, around 14 miles from Cardiff
Mary West, a street pastor and executor of Mrs Sabine's will, said in written evidence she had "span a myth about her life".
Mrs West added: "She had stories of winning a modelling contract in Australia, a glamorous singing career and tales of her husband's affairs.
"She took great pride in the communal garden area after her husband was gone."
The inquest, in Aberdare, continues.