A Shirehampton man threatened to "set fire to his mother until she died".
George Cassel was suffering from a substance abuse-induced mental health disorder when he made the chilling statement, Bristol Crown Court heard.
A jury found the 24-year-old, of Watling Way, guilty of making a threat to kill.
After considering two doctors' reports Judge James Patrick handed him a hospital order involving mental health treatment.
Judge Patrick told the court Cassel was convicted for affray in July 2017 - he had a knife in a public place and received a suspended jail term.
'A tirade of abuse'
Early this year Cassel left his undergraduate course and returned home, the court heard.
But the judge described how, in March, Cassel accompanied his mum on a shopping trip and trouble flared.
The judge said: "You subjected her to a tirade of abuse and threats for a quarter of an hour.
"You threatened to murder her.
"You threatened to set her on fire until she died.
"The clue was the arrival of a necklace.
"When a necklace and bow and arrow was delivered to her home she called the police."
The court heard Cassel was receiving treatment for his mental health and was compliant.
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