A Koonawarra woman who endangered the life of a stolen marmoset monkey by hiding it in her bedroom has told a court she thought it was a possum.Cheeky the marmoset was found at Brooke Mason's Illabunda Cres house just days after it was stolen from Nowra Wildlife Animal Park on October 30.Police raided the house on November 1 after an anonymous tip-off, discovering the monkey wandering freely around the 20-year-old's bedroom.Mason has since claimed she thought the exotic marmoset - which sports a thick, black and white mottled coat and white tufts of fur either side of its head - was in fact a possum.Yesterday she told Wollongong Local Court she was asked by an unnamed friend to mind the "possum" for a few days."I thought it was a possum ... I was minding it for a friend," she told Magistrate Les Mabbutt before admitting that "it was very stupid of me".Mason told the court a friend had dropped it off and she had taken care of it for two nights while waiting for someone to come and pick it up.Before that could happen, police raided the house and retrieved the scared monkey, with the help of Nowra Wildlife Park zookeeper Trent Burton.Despite being stressed, Cheeky responded to a training drill and was easily recaptured before being taken back to the animal park and reunited with family.Mason was subsequently arrested and charged with having stolen goods in custody.Yesterday she pleaded guilty to the offence, though she still claimed to have mistaken Cheeky for a possum.She also entered guilty pleas to charges of refusing to pay for accommodation and larceny, both of which were associated with an unrelated matter on September 19.Sentencing Mason, Mr Mabbutt noted the only other offence on her record was a minor drug possession charge.He said it was lucky for Mason the monkey was not harmed, but he found it difficult to accept Mason's "possum" story."Nothing in the facts suggest you harmed the monkey ... (though) your claim that you thought it was a possum doesn't really assist you."Noting that a $500 fine was the maximum penalty for having a monkey in custody, Mr Mabbutt fined Mason $450 and ordered her to pay court costs.