A paramedic from London accused of killing his baby son lost his temper with the boy's twin sister, a family friend has told the Old Bailey.
Gavin Gibbs raised his voice and adopted "an angry tone", said Karen Smith, who added she felt "quite uncomfortable" afterwards.
Mr Gibbs, 41, from Erith, south-east London, denies murdering three-month old Charlie in October 2008.
He also denies causing the baby and his twin grievous bodily harm with intent.
Mrs Smith knew Mr Gibbs because her husband, Murray, was his ambulance partner.
"The girl wasn't feeding very well and Gavin got angry with her," Mrs Smith told the trial.
"He tried to feed her and she was still acting like she didn't want to take the bottle.
"He raised his voice," she added. "I can't remember exactly what he said. It was an angry tone.
"I felt quite uncomfortable so I turned away."
The girl - who cannot be identified for legal reasons - spent time in hospital with a chest infection and at one stage was also found to have four broken ribs.
The court also heard from two neighbours who said they had heard the babies screaming in the middle of the night, about three weeks before Charlie's death.
"I heard one of them really, really crying - screaming, if you like. It was a piercing cry," said Rae Love.
"We went out again one-and-a-half hours later, and the second baby had started crying as well.
"I was upset by it. It was shrill and unnerving."
Her daughter Terry described hearing "a painful cry".
Mr Gibbs is alleged to have broken Charlie's arm and also caused other injuries, including a fractured skull and a broken leg.
The trial continues.