Just saw this for the first time - great movie, but I'm a little confused about how the two guitar cases got switched. Was this just something that was left unexplained, or did I just miss something?
Mariachi tucks his case under the barstool and then goes back to the motel to get his money back. Azul comes into the bar and sets his case under the barstool and orders a beer. Then he picks up a case, the wrong one, and leaves. Mariachi comes back in and picks up Azul's case and immediately notices that it doesn't feel right.
The Mariachi, being an artist and all that, is more sensitive.
Alternative explanation: The guitar case weighs the same all the time while the weight of the arms case changes with the contents. So the Mariachi was used to feel a particular weight while Azul was not.
It's kind of a plot hole that Azul did not notice that his suitcase was lighter. A spanish guitar is pretty light, I would guess that a suitcase full of guns and knives would weight at least 10 times more. That's not a sensitivity issue, that's just stuff a 4 year old can tell apart.
Maybe Azul thought that he he got used to the weight of his guitar case after he sat down and built some muscle after all the time he's carrying the guitar case. Lol, just joking.
I don't know if they made it confusing or didn't show it clearly on purpose, but this is one of those inconsistencies that really annoys you and makes you try to remember when did it happen, instead of relaxing and watching the movie.