Several experts told the court that the injuries match to that of movement involving "acceleration and deceleration" - or shaking.
A medical expert said the baby had suffered extensive retinal haemorrhages in the back of his eyes.
In a confronting police interview played to the court, Detective Jeff Foley explained to the carer the seriousness of the baby's injuries, asking her if she could explain how they happened.
She said the only thing she could think of were when the baby's 2-year-old brother and another child, also in her care, were running circuits around the house and collided, with the baby's brother landing on top of him while in the bouncy-net.
The carer said she saw him roll off the baby and the bouncer "came up and down a bit", but he seemed "okay" when she checked him.
When asked why she didn't mention it in a previous police interview, she told Detective Foley she didn't want the baby's brother getting into trouble or being blamed.
The carer mentioned another instance where the baby had toppled backwards over her leg while sitting on a grassy area at her home on January 23. But upon checking him, she noticed nothing out of the ordinary.
However Foley told the carer that they had relayed that information back to medical experts who said both instances of the bouncy net and the fall on the grass were "extremely unlikely" to cause the injuries.
He compared them to that of a car accident or a serious fall and asked the carer if she had ever shaken or thrown the baby while he was in her care.
"I haven't shaken him, I haven't dropped him or thrown him," she replied tearfully.
Judge Rea has reserved his decision for Tuesday, asking for written submissions from both the prosecution and defence.
