According to Professor David Alais from the University of Sydney’s school of psychology, who spoke to the Guardian , however, the illusion is an example of a "perceptually ambiguous stimulus" which essentially means that because the recording is ambiguous (read: a bit slurry and crap), our brain will lock onto one hearing of the recording and just go with it. How we hear it in the first place, he says, depends on a number of factors such as age (older people have less high frequency sensitivity) and accent; Australians might interpret it differently tfrom North Americans – a bit like how saying "fierce" in a British accent might sound like "face" to someone from Northern Ireland.