A few days ago I wrote abut the fun of minimal pairs (http://lozguistics.blogspot.com/2009/11/minimal-pairs-maximal-entertainment.html), and how these words can differ in the tiniest ways.
I've come across a number of lexical items from that collection that I've been worrying over. I just can't hear the different. Take 'minute' and 'star' as an example pair. I can't tell the different. It's not tone, it's not aspiration, it's not vowel length.
That's because these two aren't minimal pairs, but homophones. That is, they're both 'karmu'. Likewise 'song' and 'put' are both 'lu'. Here I was trying to make life hard for myself when the answer was really very simple.