How do I explain nasal vowels to someone learning French?

blurb   Mon May 10, 2010 11:30 am GMT
A friend of mine is learning French. Her pronunciation is almost perfect, apart from her nasal vowels. She always pronounces the "n" or "m", and seems to be incapable of pronouncing a nasal vowel without following it by a nasal consonant. For example, she pronounces "chantant" as [ʃɑ̃ntɑñ] instead of [ʃɑ̃tɑ̃]. How would you explain the difference to someone who has no concept of nasal vowels?
blurb   Mon May 10, 2010 11:31 am GMT
[ʃɑ̃ntɑ̃n], not [ʃɑ̃ntɑñ]
PARISIEN   Mon May 10, 2010 1:42 pm GMT
Very simple: stop emitting the vowel just at the moment the "n" sound is going to be audible!

In other words, when the tongue is about to touch the palatal cavity.
blurb   Mon May 10, 2010 1:59 pm GMT
I've tried that, but she instinctively denasalizes it in that case because she already knows that she's not going to say the "n". I'm starting to wonder whether it's just stubbornness on her part.