Illabial

Lazicius identifies the second part of this interjection with the long high open phoneme y· (as occurring in fy· 'grass'). This interpretation is certainly incorrect since this interjectional ɯ is illabial, whereas y is rounded.

More refined analyses show that there are differences in the misperception of certain vowels between children and adults. For example, illabial /e:/ tends to be confused with labial /0:/ in adults' perception...

Newer studies do not offer any solution to the problem. They are even less informative in that they usually just mention the existence of rare labial variants and the quantitative predominance of illabial ones.