William Tyrrell's foster mother has told a NSW coroner she heard a high-pitched and muffled "scream" minutes after the three-year-old vanished in September 2014.
The woman also testified she thought he'd been snatched when it went quiet while the boy, dressed as Spiderman, was playing "daddy tiger".
"I couldn't hear a thing. It was silent. There was no wind. There were no birds," the foster carer said on Tuesday at a Sydney inquest into William's disappearance and suspected death.
She said sound carries "unbelievably" well in the little village of Kendall, on the mid north coast, and "you can hear everything".
She stood in the backyard of her mother's house wondering why she couldn't hear William or see his costume as "it hasn't been that long".
"My immediate thought was somebody has taken him and he's gone," she said.
The woman, who cannot be identified, said she heard "like a scream" while searching for William near long grass.
"When a child hurts themselves unexpectedly, there's a scream. And it felt like a scream. And it was quick, and it was high-pitched and it was sharp," she said.
"I got into the bush and I thought ... maybe I imagined it, maybe it was a bird."
In a statement made to police, the foster mother said: "William's cry is quite distinctive when he's distressed."
"But it was quick, it was ... almost only like, three seconds and it sounded muffled."
She then called triple-zero at 10.56am, estimating he had gone missing at 10.30am.
The last photo of William was taken at 9.37am.
On Monday, the foster mother said she saw three cars on the street the morning he disappeared - including one white and one grey car parked between two driveways.
Continuing her evidence on Tuesday, the woman said she didn't realise until after William went missing that those two cars were gone.
"In the initial stage (of searching), it didn't even occur to me those cars weren't there," she said.
Neighbours quickly helped to look for William, with some posting on Facebook for assistance while others did line searches with the SES or brought in their quad bikes, the coroner heard.
Anne Maree Sharpley said the foster mother was "rather upset" and told her words to the effect of: "He's either hit his head and can't answer me or somebody's taken him because he knows to answer me."
Another testified her young daughter called out for William because "I thought by now he would be scared (and) maybe he would respond to a little person".
William's foster father, biological parents and police are due to give evidence for the remainder of the week.
Further hearings will run in August when persons of interest will be called to testify.
Counsel assisting the coroner, Gerard Craddock SC, said he expected the evidence would altogether establish William "was taken" and his disappearance "was the direct result of human intervention".
The inquest before Deputy State Coroner Harriet Grahame continues.
Australian Associated Press