A youth jail guard told an inquest into the death of a teenager how the boy was left with vomit on his face and his eyes "bulging" after he was restrained.
Gareth Myatt died just three days into his sentence
Gareth Myatt, from Staffordshire, died aged 15 at Rainsbrook training centre, Northamptonshire, in April 2004.
He was held down by Diana Smith, Dave Bailey and Dave Beadnall using a Home Office-approved restraint.
Mrs Smith told the inquest she only realised something was wrong after Gareth had "settled down".
Gareth choked on his vomit and asphyxiated, a post-mortem examination found.
The inquest in Irthlingborough, Northamptonshire, heard the teenager was restrained when he lunged at an officer during a row over the cleaning of a toasted sandwich maker.
Gareth, who died three days into his sentence, was held using the then Home Office-approved Seated Double Embrace (SDE) restraint. The restraint has since been banned.
Mrs Smith said she sat on Gareth's left hand side and a colleague sat on the right to control his arms and legs as he sat on his bed.
She told the inquest the boy continued to be aggressive as he was restrained.
She said: "Gareth was doing a lot of shouting and swearing.
"He did say at one stage that he couldn't breathe. Somebody said 'if you're shouting you can breathe'."
Mrs Smith told the inquest Gareth then appeared to settle down and she realised there was something wrong.
She said: "I just saw this stuff on his face and he looked as if his eyes were bulging.
"I can't remember, I've tried to put it out of my mind."