I found this funny for the same reason. I focus every time I say sleep so I don't say stupid lol
This always sounds phonetically like "mu" instead of "ngyu" to me. Any recommendations on distinguishing the sounds or is it the recording?
The tone on ngủ has a falling-rising intonation mostly in Southern Vietnamese, and also in some other dialects in the North. But in Hanoi (Northern Vietnamese, which this course is based on), the so-called hỏi tone is indeed slightly falling. To me, personally, it is very difficult to distinguish ngủ and ngù, both are falling.
Words with a hoi often start at a lower tone... Huyen fall slowly from a mid tone. Nang drops fast from a mid tone.