The book about the wonky donkey adds a new adjective every few pages, ending with "spunky, hanky-panky cranky stinky dinky lanky honky-tonky winky wonky donkey".
The Scottish granny finds the adjectives hilarious and giggles her way through the book.
"Oh dear, how can anybody read this seriously," she says at one point. "This is going to kill me."
The video has been viewed more than three million times in the past week alone.
The Kiwi author of the book told the Guardian that his publisher is "rushing to print another 50,000 copies, with a view for more" as demand for the book has soared since the video hit the internet.
The book, illustrated by Katz Cowley, had already sold more than one million copies before the online video turned it into a sold-out bestseller.
"The video is gold. Watching Janice read and laugh was just delightful, and like many, her infectious laugh had me laughing too," Smith told the Guardian.
"I've always wondered why sales had not taken off so much in the UK and US, but that looks like that's about to change."
"I am so glad that Wonky's reputation has finally come to bite him on the bum on this side of the world thanks to 'Wonky's Guardian Granny'. I couldn't be more delighted," Smith added.
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