"can / can't"

Just as an aside. The New Zealand pronunciation is similar to BrE in that the two different vowel sounds mean that the words are very seldom confused or misheard. However, many Australians pronounce words like "dance" and "chance" closer to the US sound than the NZ/Br, and similarly, to my ears, the vowel sound in "can't" sometimes approximates that in "can" in rapid speech. I've heard people ask for clarification.
a) "I went to the doctor, he said I can't come to work on Monday".
b)"You can or you can't?"
a) "I can't".

not a teacher