It is "highly improbable" that a baby put a wad of tissues down his own throat and rendered himself unconscious, a medical expert has told a court.
Luke Paul Szabo is on trial in the ACT Supreme Court, accused of stuffing the tissues down the baby's throat in June last year because the 11-month-old was crying. The Canberra chef was babysitting the infant and four other children at the time.
Mr Szabo denies the allegations and has pleaded not guilty to inflicting grievous bodily harm and choking or suffocating the baby. He claims to have acted desperately to save the baby's life after finding the infant choking on the tissues.
On Friday, prosecution witness Dr Catherine Sansum told the court 11-month-old babies had the ability to put objects in their mouths.
But she said a child of that age did not have the capacity to create a wad of four tissues, which is what forensic evidence suggested was to blame for obstructing the baby's airways in this case.
Dr Sansum also said that if a baby put tissues in their mouth, they would not try and push them further in.
"Once an 11-month-old baby has something in their mouth that's unpleasant, they try to spit it out or they gag on it," she said.
Dr Sansum also cast doubt on whether other injuries sustained by the baby could have been caused by Mr Szabo conducting CPR.
Professor Johan Duflou, called on by the defence, countered Dr Sansum's evidence on Friday.
He told the court: "If they can place one [tissue] in their mouth, they can place four in their mouth as far as I'm concerned."
He maintained it was entirely possible the infant could have accidentally choked himself.
But, when questioned about whether it would have become increasingly difficult for the baby to keep stuffing tissues in his mouth, Professor Duflou said he couldn't say either way.
Professor Duflou said the baby's injuries could feasibly be explained by Mr Szabo's attempts to save the infant's life.
The trial continues.