The Office star Ricky Gervais' first children's book is set to become his latest hit - but with adult comedy fans proving the most eager audience.
Gervais has created a cast of fictional animals, like the Grundit
Flanimals, about his menagerie of made-up creatures, has had its initial 100,000 print run extended even before its official release on Thursday.
Online retailer Amazon says it is also riding high in its charts.
But Amazon says most buyers are fans of alternative comedy, and not parents buying it for their children.
In the book, Gervais introduces a range of grotesque and bizarre animals such as the munty flumple, wobboid mump and munge fuddler.
Publishers Faber and Faber said the print run was "certainly far greater than a standard children's book".
At 1100 BST, it was at number five in Amazon.co.uk's book chart.
An Amazon spokeswoman said the firm could tell what types of people were putting in orders - and it was not the usual children's market.
"It's interesting to see that it doesn't seem to be mums who are buying them for their kids," she said.
"It seems to be fans of alternative comedy and fans of The Office and Little Britain and Monty Python. It seems to be fans of Ricky Gervais and his work."
The Amazon site shows the next most popular book among people who bought Flanimals is not another children's publication - but Grumpy Old Men: The Official Handbook.
Gervais says he has been interested in zoology since he went to university to study biology but changed courses after two weeks to avoid the 9am lectures.
"I've been trying to do the book for about six years, but nobody answered the door until I knocked on it with four Baftas."
He has been the UK's most successful new comedy star of the decade so far, starring in, co-writing and co-directing BBC sitcom The Office.
He has won the Bafta award for best comedy performance for three years in a row, while The Office took two Golden Globes in Hollywood in January.